# Association between migration and severe maternal outcomes in high-income countries: Systematic review and meta-analysis

Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Zelda Stewart, Agnès Dechartres, Catherine Deneux-Tharaux

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Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Zelda Stewart, Agnès Dechartres, et al. As-sociation between migration and severe maternal outcomes in high-income countries: Systematic re-view and meta-analysis. PLoS Medicine, 2023, 20 (6), pp.e1004257. 10.1371/journal.pmed.1004257. hal-04171381

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RESEARCH ARTICLE

# Association between migration and severe maternal outcomes in high-income countries: Systematic review and meta-analysis

Maxime Eslier<sup>1,*</sup>, Elie Azria<sup>1,2,*</sup>, Konstantinos Chatzistergiou<sup>1,2</sup>, Zelda Stewart<sup>1,†</sup>, Agnès Dechartres<sup>1,§</sup>, Catherine Deneux-Tharaux<sup>1</sup>

1 Université Paris Cité, CRESS, Obstetrical Perinatal and Pediatric Epidemiology Research Team, EPOPé, INSERM, INRAE, Paris, France, 2 Maternity Unit, Paris Saint Joseph Hospital, FHU PREMA, Paris, France,

3 Sorbonne Université, INSERM, Institut Pierre Louis d'Epidémiologie et de Santé Publique, AP-HP. Sorbonne Université, Hôpital Pitié-Salpêtrière, Département de Santé Publique, Paris, France

© These authors contributed equally to this work.

* maxime.eslier@inserm.fr

<figure><img src="image_2.png" /></figure>

## Abstract

<figure><img src="image_3.png" /></figure>

### OPEN ACCESS

**Citation:** Eslier M, Azria E, Chatzistergiou K, Stewart Z, Dechartres A, Deneux-Tharaux C (2023) Association between migration and severe maternal outcomes in high-income countries: Systematic review and meta-analysis. PLoS Med 20(6): e1004257. https://doi.org/10.1371/journal.pmed.1004257

**Received:** September 13, 2022

**Accepted:** June 5, 2023

**Published:** June 22, 2023

**Peer Review History:** PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pmed.1004257

**Copyright:** © 2023 Eslier et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

**Data Availability Statement:** All relevant data are within the manuscript and its Supporting Information files.

**Funding:** The authors received no specific funding for this work.

### Background

Literature focusing on migration and maternal health inequalities is inconclusive, possibly because of the heterogeneous definitions and settings studied. We aimed to synthesize the literature comparing the risks of severe maternal outcomes in high-income countries between migrant and native-born women, overall and by host country and region of birth.

### Methods and findings

Systematic literature review and meta-analysis using the Medline/PubMed, Embase, and Cochrane Library databases for the period from January 1, 1990 to April 18, 2023. We included observational studies comparing the risk of maternal mortality or all-cause or cause-specific severe maternal morbidity in high-income countries between migrant women, defined by birth outside the host country, and native-born women; used the New-castle-Ottawa scale tool to assess risk of bias; and performed random-effects meta-analyses. Subgroup analyses were planned by host country and region of birth.

The initial 2,290 unique references produced 35 studies published as 39 reports covering Europe, Australia, the United States of America, and Canada. In Europe, migrant women had a higher risk of maternal mortality than native-born women (pooled risk ratio [RR], 1.34; 95% confidence interval [CI], 1.14, 1.58; *p* < 0.001), but not in the USA or Australia. Some subgroups of migrant women, including those born in sub-Saharan Africa (pooled RR, 2.91; 95% CI, 2.03, 4.15; *p* < 0.001), Latin America and the Caribbean (pooled RR, 2.77; 95% CI, 1.43, 5.35; *p* = 0.002), and Asia (pooled RR, 1.57, 95% CI, 1.09, 2.26; *p* = 0.01) were at higher risk of maternal mortality than native-born women, but not those born in Europe or in the Middle East and North Africa. Although they were studied less often and with heterogeneous definitions of outcomes, patterns for all-cause severe maternal morbidity and maternal intensive care unit admission were similar. We were unable to take into account other
**Competing interests:** I have read the journal's policy and EA have the following competing interests: EA declared participation in the Data safety Monitoring board of the Betadose trial, Member of the advisory board of the Mamaact Trial and Head of the commission "Health inequalities" of the French College of Obstetrician and Gynecologists (CNGOF).

**Abbreviations:** CI, confidence interval; ICD, International Classification of Diseases; ICU, intensive care unit; RR, risk ratio; ROAM, Reproductive Outcomes and Migration; USA, United States of America; WHO, World Health Organization.

social factors that might interact with migrant status to determine maternal health because many of these data were unavailable.

## Conclusions

In this systematic review of the existing literature applying a single definition of "migrant" women, we found that the differential risk of severe maternal outcomes in migrant versus native-born women in high-income countries varied by host country and region of origin. These data highlight the need to further explore the mechanisms underlying these inequities.

## Trial Registration

PROSPERO CRD42021224193.

## Why was this study done?

* Some studies conducted in high-income countries report that the risk of maternal mortality and severe maternal morbidity is higher for migrant than native-born women, while other studies do not.

* Whether this heterogeneity is related to differences in the definition and measurement of migration and of maternal outcomes or to real differences between settings remains unclear.

## What did the researchers do and find?

* In this literature review including 35 studies, we found that, in high-income countries, the differential risk of severe maternal outcomes in migrant women, defined as born outside the host country, compared to native-born women, varied by the host country and the migrant women's region of birth.

* In Europe, migrant women were generally at higher risk of severe maternal outcomes than native-born women, whereas the risks for migrant women did not differ significantly from those for native-born women in United States of America or Australia.

* Among migrant women, those born in sub-Saharan Africa, in Latin America and the Caribbean, or in Asia were at higher risk of severe maternal outcomes than their native-born counterparts, while those born in Europe or in the Middle East and North Africa were not.

## What do these findings mean?

* When a single definition of "migrant" women was applied, the differential risk of severe maternal outcomes in migrant versus native-born women in high-income countries varied by host country and region of origin.

* These data highlight the need to further explore the mechanisms underlying these inequities.

* Future studies should use harmonized definitions for all-cause and cause-specific severe maternal morbidity and take into account other social factors such as race/
ethnicity, migrant women's administrative status, and economic factors that may inter-
act with migration to understand the inequalities in maternal health between migrant
and native-born women.

**Introduction**

Economic crises, wars, natural disasters, and increased inequalities between countries have generated significant migration waves. Over the past decade, the migrant population has increased by 23% in countries belonging to the Organisation for Economic Co-operation and Development [1] and by 28% in the European Union [2]. These movements, involving large proportions of young adults, women in particular [2], result in increasing the proportion of births to foreign-born women in their host countries. In Europe, every fourth birth is to a foreign-born mother, although this rate varies substantially across countries [3,4]. This trend presents organizational and cost challenges for the host health systems, especially as migrant women appear to be more vulnerable and to have greater social and health needs than native-born women [5,6].

Because the scientific literature on the association between migration and severe maternal outcomes is heterogeneous and inconclusive, it cannot accurately inform public policies or healthcare provision [7]. Some studies in high-income countries have reported higher risks of maternal mortality and severe maternal morbidity among migrant women than native-born women [8–13], while others have not [14–17]. Whether this heterogeneity is related to differences in definitions and methods of measuring migration and maternal outcomes or to real differences between settings remains unclear. Studies have defined migrant women according to their race or ethnicity [18–23], nationality [24–27], or their birthplace [14,16,17,28–33]. A few others have used other criteria, such as the Human Development Index of the country of origin [34], length of residency in the host country, or legal status [35]. The Reproductive Outcomes and Migration (ROAM) collaboration and the EURO-PERISTAT project recommended that maternal country of birth be used to study immigrants’ perinatal health [36]. The severe maternal outcomes targeted and their definitions also vary greatly across studies. Moreover, because much of the available literature is based on routinely collected data coded by the International Classification of Diseases (ICD), severe maternal outcomes might well be misclassified [14,15,17,37–43]. A previous review and meta-analysis of data from Western European countries between 1970 and 2013 showed that migrant women have a risk of maternal mortality twice that of women born in the host country [8]. Its results were nonetheless limited by the important heterogeneity in the definitions of migrant women across studies and the inclusion of old data. Another systematic review also conducted on European studies compared the risk of nonsevere maternal outcomes between 2007 and 2017 for specific subgroups of migrant women only—asylum seekers and undocumented migrant women in Europe. It reported that the risk of maternal mortality and all-cause severe maternal morbidity was higher among asylum seekers than native-born women [35].

Applying a single definition of migrant women, in accordance with international recom-
mendations, we aimed to conduct a systematic review and meta-analysis of available informa-
tion about the risk of severe maternal outcomes among migrant and native-born women in
high-income countries. Differential risk was compared overall and by both host country and
migrant women's region of birth.
# Methods

## Search strategy and selection criteria

This systematic review and meta-analysis examines studies of the association between migration and severe maternal outcomes in high-income countries. The review protocol was registered with the PROSPERO International Prospective Register of Systematic Reviews, on its website (CRD42021224193), and this article is reported according to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines [44].

We searched Medline via PubMed, Embase, and Cochrane Library without language restriction. The search algorithm included relevant Medical Subject Headings (MeSH)/Embase Medical Headings (EMTREE) and free text words combined by Boolean operators for migrant and selected severe maternal outcomes (list below) (S1–S3 Tables). We also screened the reference lists of previous systematic reviews and meta-analyses and of all included studies for any additional references.

We included observational studies published between January 1, 1990 and April 18, 2023, and comparing the risk of severe maternal outcomes between migrant women and native-born women in high-income countries, according to the World Bank classification. Systematic reviews and meta-analyses were included in the first selection by titles and abstracts to allow backward snowballing but excluded in the second selection. Case-control and case studies were excluded. The exclusion of studies before 1990 aimed to limit the heterogeneity in migrant women's characteristics and host countries' integration policies that could be caused by too long a study period.

Our review included studies that defined migrant women as women born outside the host country and compared them with women born in the host country, in accordance with international recommendations [36,45,46]. The severe maternal outcomes studied were maternal mortality, all-cause severe maternal morbidity, and cause-specific severe maternal morbidity, during pregnancy and up to 1 year after delivery. The specific causes of severe maternal morbidity included were severe postpartum hemorrhage, eclampsia, severe sepsis, and uterine rupture, as well as maternal intensive care unit (ICU) admission and near misses, as defined by the World Health Organization (WHO) [47]. This review did not consider maternal mental health outcomes because we believe they require a specific assessment and because a systematic review on this topic was registered as underway when we started (PROSPERO, CRD42021226291) and finally published [48].

We used Covidence systematic review software (Veritas Health Innovation, Melbourne, Victoria, Australia) to screen and extract data. Two reviewers (ME and KC) independently screened first the titles and abstracts of the retrieved studies to exclude those that were irrelevant and then the full text of the remaining studies to assess eligibility for inclusion. Disagreements were resolved through discussion with the help, if necessary, of a third author (EA or CDT) to reach a consensus. Reasons for exclusion were recorded. The corresponding author of unavailable articles was contacted by email to request the full text version.

## Data analysis

The same reviewers (ME and KC) independently extracted the following characteristics for each included study: general study information (authors' names, year of publication, journal, language, funding); study characteristics (study design, population coverage, inclusion period, host country, and data source for the exposure of interest and for outcomes); characteristics of the study population (total number of women, inclusion/exclusion criteria); outcomes evaluated (mortality and/or all-cause severe maternal morbidity and/or cause-specific severe
maternal morbidity); number of cases overall, in each subgroup and for each outcome of interest; and items to assess methodological quality. We contacted corresponding authors to obtain additional data not available in the original publication.

Two authors (ME and KC) used the Newcastle-Ottawa scale for observational studies to assess the methodological quality of each study and based their assessment on the following categories of items: selection of study groups, comparability of groups, and ascertainment of the outcome of interest [49]. The threshold for defining a high-quality study was a score $\ge$7 [50].

An unadjusted risk ratio for each outcome was estimated with the number of events and of migrant women and native-born women reported in each study. We did not estimate adjusted risk ratios because this study examined the differential risk between migrant women and native-born women and not causal mechanisms. Between-study heterogeneity was explored by visual examination of the forest plots and by the heterogeneity test and $I^2$ statistic with its 95% confidence interval (CI) [51,52]. Because heterogeneity was expected on scientific grounds, we used random-effects meta-analysis models with the DerSimonian and Laird method [51] and decided, when relevant, not to provide an overall assessment and to combine data only within subgroups. Those subgroups were defined according to the host country (European countries, the United States of America (USA), Canada, and Australia), the migrant women's regions of birth (Europe, the Middle East and North Africa, sub-Saharan Africa, Latin America and the Caribbean, and Asia and the Pacific), the migrant women's legal status (migrant women with host country nationality, legally resident migrant women without host country nationality, and undocumented migrant women), and the Newcastle-Ottawa scale score. We tested the interaction between the exposure of interest and the variables defining subgroups. The considerable heterogeneity in definitions of cause-specific severe maternal morbidity prevented the performance of any quantitative meta-analysis for these outcomes.

We assessed small-study effects with funnel plots when there were sufficient studies ($n > 10$).

Analyses were done with Review Manager Software (version 5.4.1).

# Results

## Characteristics and methodological quality assessment

Of the 2,290 records screened, 185 were relevant for full-text review and 39 were finally included (Fig 1). The appendix provides a list of excluded studies with the reasons for their exclusion (S4 Table). The leading reason for exclusion was the absence of a definition of migration based on region of birth, followed by outcomes outside the scope of our review.

Table 1 shows the characteristics of the 35 studies from Europe, Australia, the USA, and Canada that furnished 39 reports. Because 4 studies yielded several reports covering different outcomes or different subgroups of migrant women, we included 39 reports overall. The median year of publication was 2017 (range 2008 to 2022). Half the studies used the ICD or procedure codes to define their outcomes (Tables 1 and S5). The assessment of the quality of the studies included is presented in the appendix (S6 Table). According to the Newcastle-Ottawa scale score, only 1 study had a low methodological quality that limited the relevance of the subgroup analysis (Tables 1 and S6). Because only 3 studies contained information about legal status, we did not perform the corresponding subgroup analysis (Table 1).

## Maternal mortality

Seventeen highly heterogeneous studies included data on maternal mortality (S1 Fig). In European host countries, migrant women were at higher risk of maternal mortality than native-
<figure><img src="image_4.png" /><figcaption>Fig 1. Study selection.</figcaption></figure>

https://doi.org/10.1371/journal.pmed.1004257.g001

born women (pooled risk ratio [RR] 1.34; 95% CI, 1.14, 1.58; *p* < 0.001; *I*² = 58%; 95% CI, 18, 79), with RR ranging from 0.77 (95% CI, 0.15, 3.80) to 2.01 (95% CI, 1.53, 2.65), whereas no excess risk was observed in the USA or Australia (*p* for interaction < 0.001) (Fig 2). Some subgroups of migrant women were at higher risk of maternal mortality than their native-born counterparts. They included women born in sub-Saharan Africa (pooled RR, 2.91; 95% CI, 2.03, 4.15; *p* < 0.001; *I*² = 57%; 95% CI, 0, 83), in Latin America and the Caribbean (pooled RR, 2.77; 95% CI, 1.43, 5.35; *p* = 0.002; *I*² = 82%; 95% CI, 53, 93), and in Asia (pooled RR, 1.57; 95% CI, 1.09, 2.26; *p* = 0.01; *I*² = 31%; 95% CI, 0, 74). Women born in Europe or in the Middle East and North Africa, on the other hand, were not at higher risk (*p* for interaction < 0.001) (Fig 3). Among European countries, the United Kingdom, Denmark, Norway, and Spain presented a particular pattern, with no significant excess risk of maternal mortality for migrant women considered globally (Fig 2), but specific subgroups studied according to their region of birth did show such an excess risk compared to native-born women (Fig 3).

## All-cause severe maternal morbidity

Similar patterns were found for both all-cause severe maternal morbidity and maternal ICU admission. The meta-analysis of the former included 10 studies comparing migrant women and native-born women with substantial heterogeneity (Figs 4, 5 and S2). The pooled relative risk of all-cause severe maternal morbidity in migrant women compared to native-born women was 1.19 (95% CI, 0.95, 1.49; *p* = 0.1; *I*² = 87%; 95% CI, 69, 95) in European host countries and 0.99 (95% CI, 0.95, 1.03; *p* = 0.7; *I*² = 83%; 95% CI, 64, 92) in the USA and Australia (*p* for interaction < 0.001) (Fig 4). Among migrant women, those born in sub-Saharan Africa (pooled RR, 1.54; 95% CI, 1.26, 1.88; *p* < 0.001; *I*² = 88%; 95% CI, 72, 95) or in Latin America and the Caribbean (pooled RR, 1.14; 95% CI, 1.05, 1.25; *p* = 0.003; *I*² = 51%; 95% CI, 0, 84)
<table><caption>Table 1. Characteristics of included studies.</caption><thead><tr><th></th><th></th></tr></thead><tbody><tr><td>Total = 35 studies</td><td></td></tr><tr><td>First year of inclusion period, median (min-max)</td><td>2007 (1988–2016)</td></tr><tr><td>Last year of inclusion period, median (min-max)</td><td>2012 (2005–2019)</td></tr><tr><td>Host country, n (%)</td><td></td></tr><tr><td>Australia</td><td>7 (20)</td></tr><tr><td>United States of America</td><td>5 (14)</td></tr><tr><td>France</td><td>4 (11)</td></tr><tr><td>Canada</td><td>4 (11)</td></tr><tr><td>the Netherlands</td><td>3 (9)</td></tr><tr><td>United Kingdom</td><td>3 (9)</td></tr><tr><td>Sweden</td><td>2 (6)</td></tr><tr><td>Denmark</td><td>2 (6)</td></tr><tr><td>Germany</td><td>2 (6)</td></tr><tr><td>Norway</td><td>1 (3)</td></tr><tr><td>Spain</td><td>1 (3)</td></tr><tr><td>Italy</td><td>1 (3)</td></tr><tr><td>Multicountry</td><td>1 (3)</td></tr><tr><td>Study population, n (%)</td><td></td></tr><tr><td>National</td><td>21 (60)</td></tr><tr><td>Regional</td><td>9 (26)</td></tr><tr><td>Mixed (National and Regional)</td><td>1 (3)</td></tr><tr><td>Multicenter</td><td>2 (6)</td></tr><tr><td>Single-center</td><td>3 (9)</td></tr><tr><td>Study design, n (%)</td><td></td></tr><tr><td>Cohort study</td><td>19 (54)</td></tr><tr><td>Cross-sectional study</td><td>17 (49)</td></tr><tr><td>Source of information regarding exposure of interest*, n (%)</td><td></td></tr><tr><td>Birth and/or death certificates</td><td>29 (83)</td></tr><tr><td>Birth register</td><td>4 (11)</td></tr><tr><td>Interview</td><td>1 (3)</td></tr><tr><td>Medical file</td><td>1 (3)</td></tr><tr><td>Self-administered questionnaire</td><td>1 (3)</td></tr><tr><td>Legal status available, n (%)</td><td>3 (9)</td></tr><tr><td>Reported outcome, n (%)</td><td></td></tr><tr><td>Maternal mortality</td><td>17 (49)</td></tr><tr><td>All-cause severe maternal morbidity</td><td>10 (29)</td></tr><tr><td>Maternal near miss</td><td>3 (9)</td></tr><tr><td>Maternal intensive care unit admission</td><td>5 (14)</td></tr><tr><td>Eclampsia</td><td>4 (11)</td></tr><tr><td>Severe postpartum hemorrhage</td><td>6 (17)</td></tr><tr><td>Severe sepsis</td><td>4 (11)</td></tr><tr><td>Uterine rupture</td><td>8 (23)</td></tr><tr><td>Definition of outcome, n (%)</td><td></td></tr><tr><td>Clinical criteria specifically collected</td><td>18 (51)</td></tr><tr><td>Existing ICD or procedure codes</td><td>18 (51)</td></tr><tr><td>Source of information regarding outcome, n (%)</td><td></td></tr><tr><td>Medico-administrative data</td><td>15 (43)</td></tr><tr><td>Medical file</td><td>19 (54)</td></tr></tbody></table>

(Continued)
<table><caption>**Table 1.** (Continued)</caption><tr><td colspan="2">Total = 35 studies</td></tr><tr><td>Birth register</td><td>2 (6)</td></tr><tr><td>Newcastle-Ottawa scale score, median (min-max)</td><td>7 (6-8)</td></tr></table>

*Migrant women defined by region of birth.

https://doi.org/10.1371/journal.pmed.1004257.t001

were at higher risk of all-cause severe maternal morbidity than their native-born counterparts, while those born in Europe or the Middle East and North Africa were not (p for interaction < 0.001) (Fig 5).

## Cause-specific severe maternal morbidity

Only a few studies considering specific causes or conditions of severe maternal morbidity were available (Figs 6–11). The synthesis of their results was difficult given the persisting heterogeneity in outcome definitions, except for maternal ICU admission (Fig 6). Three of 5 studies reported that migrant women were at higher risk of maternal ICU than native-born women with relative risks ranging from 1.34 (95% CI, 1.23, 1.46) to 1.97 (95% CI, 1.55, 2.52) (Figs 6 and S3). Migrant women born in sub-Saharan Africa, in Latin America and the Caribbean, and in Asia were also at higher risk of maternal ICU admission than native-born women, but those born in Europe or in the Middle East and North Africa were not (p for interaction < 0.001) (S4 Fig).

<figure><img src="image_5.png" /><figcaption>**Fig 2.** Maternal mortality in migrant women and native-born women, stratified by host country. Unadjusted RRs are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RRs with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RRs. The CI is shown with lines. References: Deneux-Tharaux et al. 2017 [29]; Saucedo et al. 2021 [53]; Knight et al. 2015 [54]; Knight et al. 2017 [55]; Knight et al. 2020 [56]; Diguisto et al. 2022 [57]; Esscher et al. 2013 [28]; Garcia-Tizon Larroca et al. 2022 [58]; Schutte et al. 2009 [32]; Kallianidis et al. 2022 [59]; Johnson et al. 2014 [60]; Humphrey et al. 2015 [61]; Humphrey et al. 2017 [62]; Humphrey et al. 2020 [63]; Creanga et al. 2012 [16]; Singh et al. 2021 [14]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

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<figure><img src="image_6.png" /><figcaption>**Fig 3.** Maternal mortality in migrant women and native-born women, stratified by migrant women's region of birth. Unadjusted RRs are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RRs with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RRs. The CI is shown with lines. References: Deneux-Tharaux et al. 2017 [29]; Saucedo et al. 2021 [53]; Knight et al. 2015 [54]; Knight et al. 2017 [55]; Knight et al. 2020 [56]; Garcia-Tizon Larroca et al. 2022 [58]; Schutte et al. 2009 [32]; Kallianidis et al. 2022 [59]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

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A funnel plot was performed only for maternal mortality, as it was the only outcome for which a sufficient number of studies was available. It suggests a small-study effect (S5 Fig), which may be partly explained by the heterogeneity across host countries (S6 Fig).

## Discussion

In high-income countries, the differential risk of severe maternal outcomes between migrant and native-born women, defined as women born outside and in the host country, varied by both host country and the migrant women's region of birth. Migrant women in European host countries were at higher risk of severe maternal outcomes than native-born women, while migrant women in the USA and Australia did not differ from those born there for such outcomes. Migrant women born in sub-Saharan Africa, in Latin America and the Caribbean, or
<figure><img src="image_7.png" /><figcaption>**Fig 4.** All-cause severe maternal morbidity in migrant women and native-born women, stratified by host country. Unadjusted RR s are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RR s with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RR s. The CI is shown with lines. References: Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65], and 2011 [66]; Van Hanegem et al. 2011 [67]; Zanconato et al. 2012 [33]; Urquia et al. 2015 [40] and 2017 [15]; Wanigaratne et al. 2015 [41]; Jairam et al. 2023 [68]; Mujahid et al. 2021 [17]; Wall-Wieler et al. 2020 [42]; Leonard et al. 2021 [37]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

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in Asia were at higher risk of severe maternal outcomes than the women born in their host countries, but those born in Europe or in the Middle East and North Africa were not.

Our systematic review shows that migrant women living in European host countries had a higher risk of severe maternal outcomes than the native-born women, while migrant women in the USA and Australia did not. The social structure of the native-born groups is a hypothesis that might explain this disparity between these high-income settings. In the USA and Australia, the groups with the highest maternal mortality and morbidity rates are, respectively, Black [75] and indigenous [60–63] women, both included in the native-born reference group. The maternal mortality ratio is from 3 to 6 times higher in Black than in White women in the USA [76] and in indigenous versus nonindigenous women in Australia [60–63]. Furthermore, the overall maternal mortality ratio in the USA is more than twice as high as in Europe, and this ratio for native-born US White women is double that for native-born Europeans [53,55,76]. In both the USA and Australia, therefore, the subgroups at risk of severe maternal complications appear to be related more to race or ethnicity than to migrant women’s region of birth. Thus, in these contexts, the comparison between “native” and “foreign-born” populations does not take into account the colonial history and migratory backgrounds of the now “native” populations that played a role in determining these groups’ social position and their health status.

Another interesting finding is that migrant women born in sub-Saharan Africa, in Latin America and the Caribbean, and in Asia were at higher risk of severe maternal outcomes than the corresponding native-born women of the host country, although migrant women born in Europe or in the Middle East and North Africa were not. Notably, the particular pattern observed in the United Kingdom, with no significant excess risk in migrant women versus native-born women globally, when we did not consider region of birth, highlights the importance of studying migration according to this factor. One hypothesis for this differential risk among subgroups of migrant women is that the specific migration contexts and paths of these subgroups do not carry the same risks. Migrant women born in sub-Saharan Africa, in Latin
<figure><img src="image_8.png" /><figcaption>**Fig 5.** All-cause severe maternal morbidity in migrant women and native-born women, stratified by migrant women's region of birth. Unadjusted RRs are random-effects estimates calculated by the DerSimonian and Laird method. The data markers show the unadjusted RRs with their 95% CIs. The size of the data markers indicates the weight of the study. Diamonds show the pooled unadjusted RRs. The CI is shown with lines. References: Eslier et al. 2022 [64]; Urquia et al. 2015 [40] and 2017 [15]; Wanigaratne et al. 2015 [41]; Jairam et al. 2023 [68]; Zwart et al. 2008 [9], 2010 [65], and 2011 [66]; Van Hanegem et al. 2011 [67]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

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<figure><img src="image_9.png" /><figcaption>**Fig 6.** Maternal ICU admission in migrant women and native-born women. The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Medcalf et al. 2016 [38]; Turner et al. 2020 [69]; Gulatorsen et al. 2022 [70]. CI, confidence interval; df, degrees of freedom; ICU, intensive care unit; IV, inverse variance; RR, risk ratio.</figcaption></figure>

https://doi.org/10.1371/journal.pmed.1004257.g006
<figure><img src="image_10.png" /><figcaption>**Fig 7. Near misses in migrant women and native-born women.** The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: David et al. 2019 [71]; Wahlberg et al. 2013 [72]; Reime et al. 2012 [73]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

https://doi.org/10.1371/journal.pmed.1004257.g007

<figure><img src="image_11.png" /><figcaption>**Fig 8. Eclampsia in migrant women and native-born women.** The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Reime et al. 2012 [73]; Urquia et al. 2014 [39] and 2017 [15]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

https://doi.org/10.1371/journal.pmed.1004257.g008

<figure><img src="image_12.png" /><figcaption>**Fig 9. Severe postpartum hemorrhage in migrant women and native-born women.** The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2020 [31]; Eslier et al. 2022 [64]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Reime et al. 2012 [73]; Flood et al. 2019 [74]; Turner et al. 2020 [69]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

https://doi.org/10.1371/journal.pmed.1004257.g009

<figure><img src="image_13.png" /><figcaption>**Fig 10. Severe sepsis in migrant women and native-born women.** The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2022 [64]; Wahlberg et al. 2013 [72]; Reime et al. 2012 [73]; Urquia et al. 2017 [15]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

https://doi.org/10.1371/journal.pmed.1004257.g010
<figure><img src="image_14.png" /><figcaption>**Fig 11.** Uterine rupture in migrant women and native-born women. The squares show the unadjusted RRs with their 95% CIs. The size of the squares indicates the weight of the study. The CI is shown with lines. References: Eslier et al. 2020 [31] and 2022 [64]; Wahlberg et al. 2013 [72]; Zwart et al. 2008 [9], 2010 [65] and 2011 [66]; Van Hanegem et al. 2011 [67]; Urquia et al. 2015 [40] and 2017 [15]. CI, confidence interval; df, degrees of freedom; IV, inverse variance; RR, risk ratio.</figcaption></figure>

https://doi.org/10.1371/journal.pmed.1004257.g011

America and the Caribbean, and in Asia have usually lived in the host country for less time and are more frequently disadvantaged by a language barrier, lack of legal status, social isolation, and poor housing conditions, compared with other categories of migrant women [5,28]. These cofactors may result in a more difficult access to healthcare system, especially prenatal care, which is known to be inadequate more often, in both quantity and quality, among these geographical subgroups [77,78]. Researchers have explored the association between severe maternal outcomes and other categorizations of migrant women's native countries, besides geography. One study using the World Bank classification of economies found a higher risk of maternal near misses in migrant women from low-income countries and not in those from middle- or high-income countries, compared with women born in Sweden [72]. A Spanish study used the Human Development Index of countries to report that maternal death rates were higher for migrant women from countries with the lowest Human Development Index [58]. We could not include these analyses in our review since each was unique in its categorization. These approaches, however, provide interesting insights into the causal mechanisms of health disparities among migrant women.

Another explanatory hypothesis for the differential risk we found according to the migrant women's region of birth is the possibility of discrimination against some subgroups of migrant women with physical (e.g., black skin) or cultural singularities that might activate bias among healthcare professionals and lead to differential care [13,79–81]. These discriminations may originate from individual attitudes through explicit or implicit bias but could also be driven by structural racism [82,83]. An approach that focuses on the migration issue and takes the fact of being born abroad as the only exposure variable cannot by itself provide an insight into the mechanisms of social inequalities in health between migrant and native-born women. This approach is necessary and, in our opinion, justifies the studies thus far conducted in this way and included in this systematic review. It cannot, however, be sufficient. Maternal health is influenced by the complex interaction of multiple social factors. Among these factors, socio-economic determinants, such as migrant women's administrative status, should be considered and analyzed as potential intermediate factors. Race/ethnicity, a major determinant in contexts such as the USA or Australia, even when migration is the main focus of the studies, should also be collected and included in the analysis to enable multidimensional descriptions of the groups being compared and provide deeper insight to the causal relationships with health outcomes.

To our knowledge, this is the first systematic review and meta-analysis focusing on the association of migrant women and native-born women in high-income countries with various severe maternal outcomes and according to a single and consensual definition of migrant women. In contrast to previous systematic reviews, we have included all data available from high-income countries and not only those in Europe [8,35]. This offers the opportunity to compare national contexts with various migration demographic patterns, as well as various
public policies related to migration. Use of this single, consensual definition makes it possible to address migration issues specifically, separate from overall ethnic or racial disparities, although the ethnic/racial dimension is probably one of the mechanism involved in the disparities faced by migrant women [36,45,46]. It also reduced the heterogeneity between studies and improved their comparability. This important heterogeneity in the definitions of migrant women across studies was the main limitation of a previous review and meta-analysis [8]. This definition of migrant women, as being born outside the host country, is the one used by the International Organization for Migration [84] and recommended by the Reproductive Outcomes and Migration collaboration and the EURO-PERISTAT project, to study migrants' perinatal health [36]. We were able to apply this definition for all included studies except for some Dutch studies [9,65,66] where we cannot exclude that some second-generation migrant women were included in the migrant women group. This definition offers the advantage of targeting a homogeneous group of first-generation migrants. Second-generation migrant women constitute a specific group interesting to study, but databases with available data on the parents' and grandparents' countries of birth are still too rare for a synthesis of their results to be useful. Our planned subgroup analyses enabled us to explain a part of the still substantial heterogeneity between studies. In order to explore between-study heterogeneity, we decided to perform subgroup analyses instead of meta-regression with host country and region of birth as moderators because these characteristics are closely related in the set of studies we found, resulting in collinearity in the model, likely to bias the estimates. As a consequence, we cannot totally rule out that host country and region of birth actually characterized the same subgroups of migrant women. Nevertheless, our analysis was still limited by the persistent heterogeneity in definitions of all-cause and cause-specific severe maternal morbidity. Moreover, our review may be limited by the questionable validity of administrative databases because of the uncertain quality of the reporting and the intrinsic limitations of ICD codes—both sources of potential misclassification [43]. Another limitation is that we could not take into account other social factors that may interact with migration to determine maternal health, because many of these data are unavailable. The paucity of studies with data on migrant women's legal status prevented a subgroup analysis of this variable. Finally, we cannot exclude the risk of selective outcome reporting bias within studies. Researchers may report their findings selectively by choosing to focus on selected outcomes and analyses based on the results [51].

Our findings provide valuable insights for further exploration of the causal mechanisms of maternal health inequalities by highlighting those faced by migrant women in high-income countries according to both their region of origin and the host country. Our analysis was still limited by the persistent heterogeneity in definitions of all-cause and cause-specific severe maternal morbidity. Thus, future studies should use harmonized definitions for all-cause and cause-specific severe maternal morbidity, and future investigations should examine the extent to which specific hypothesized mechanisms, related to the characteristics of the women or the healthcare system, explain the association between migrants and severe maternal outcomes in different settings. Approaches combining the joint characterization and analysis of severe maternal outcomes according to ethnicity, race, and migration could shed light on these question and help to guide policies and care.

To conclude, the differential risk of severe maternal outcomes between migrant women and native-born women in high-income countries varies by the host country and the migrant woman's region of birth. Our findings highlight the maternal health inequalities faced by migrant women in high-income countries according to their region of origin and host country. Future studies should use harmonized definitions for all-cause and cause-specific severe maternal morbidity and be designed to explore in greater depth the mechanisms of inequalities between migrant women and native-born women.
**Supporting information**

S1 Table. Literature search algorithm on Medline via PubMed.

(DOCX)

S2 Table. Literature search algorithm on Embase.

(DOCX)

S3 Table. Literature search algorithm on Cochrane Library.

(DOCX)

S4 Table. List of the excluded studies and reasons for their exclusion.

(DOCX)

S5 Table. Characteristics of the included papers, listed in alphabetical order of first authors.

(DOCX)

S6 Table. Methodological quality of the studies included (listed in alphabetical order) assessed with the Newcastle-Ottawa Scale (NOS).

(DOCX)

S7 Table. Amendments made to the protocol PROSPERO.

(DOCX)

S1 Fig. Maternal mortality in migrant women and native-born women.

(DOCX)

S2 Fig. All-cause severe maternal morbidity in migrant women and native-born women.

(DOCX)

S3 Fig. Maternal intensive care unit admission in migrant women and native-born women, stratified by host country.

(DOCX)

S4 Fig. Maternal intensive care unit admission in migrant women and native-born women stratified by migrant women's region of birth.

(DOCX)

S5 Fig. Funnel plot for studies reporting maternal mortality overall.

(DOCX)

S6 Fig. Funnel plot for studies reporting maternal mortality stratified by host country.

(DOCX)

**Acknowledgments**

The authors would like to thank Annika Esscher and Birgitta Essén (both from the Department of Women's and Children's Health, Uppsala University, Uppsala, Sweden) who supplied data about the number of deaths and maternal mortality ratios for women of reproductive age born in low-, middle-, and high-income countries and in Sweden; Ayesha Siddiqui (Université de Paris, CRESS, Obstetrical Perinatal and Pediatric Epidemiology Research Team, EPOPé, INSERM, INRA, Paris, France) who supplied data about the total number of women diagnosed with severe preeclampsia by distinguishing the women born in France from those born elsewhere in Europe; Baiju Shah (Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada; Sunnybrook Research Institute, Toronto, Ontario, Canada; Department of Medicine,
University of Toronto, Ontario, Canada) who supplied data for the total number of women with and without preeclampsia/eclampsia among each of the nonimmigrant, refugee, and other immigrant groups; Birgit Reime (Faculty of Health Safety Society, Furtwangen University, Furtwangen, Germany) who supplied data for the total number of women diagnosed with cause-specific severe maternal morbidity among native-born and migrant women in Germany between 2001 and 2007; Jessica Turner (Mater Research Institute, University of Queensland, Brisbane, Australia) who supplied data for the total number of women diagnosed with massive postpartum hemorrhage and ICU admission among refugees and women born in Australia; Joost Zwart (Department of Obstetrics and Gynaecology, Deventer Ziekenhuis, 7416 SE Deventer, the Netherlands) and Jos van Roosmalen (Department of Obstetrics and Gynaecology, Leiden University Medical Center, 2300 RC Leiden, the Netherlands) who supplied data for the total number of deliveries among Western and non-Western migrant women; Kjersti Sletten Bakken (Centre for Intervention Science in Maternal and Child Health [CISMAC], Department of Global Public Health and Primary Care, University of Bergen) who supplied data about the total number of women diagnosed with preeclampsia/eclampsia and HELLP syndrome among first-generation immigrants, second-generation immigrants, and native Norwegian-born women; Marcelo Urquia (Department of Community Health Sciences, University of Manitoba Faculty of Health Sciences, Winnipeg, Manitoba, Canada) who supplied data about the total number of women diagnosed with eclampsia according to their region of birth; Miguel-Angel Luque-Fernandez (Department of Non-Communicable Disease Epidemiology, Cancer Survival Group, London School of Hygiene and Tropical Medicine, London; and Department of Non-Communicable Disease and Cancer Epidemiology, Instituto de Investigacion Biosanitaria de Granada (Ibs.GRANADA), University of Granada, Granada, Spain) who supplied data about the total number of live births in Spain and in Europe excluding Spain; Stephanie Leonard (Department of Obstetrics and Gynecology, Stanford University, Palo Alto, California; California Maternal Quality Care Collaborative, Stanford University, Palo Alto, California) who supplied data on the total number of women with severe maternal morbidity, and with non-transfusion severe maternal morbidity in native-born women and migrant women. We would also like to thank Jo Ann Cahn for her English editorial assistance.

**Author Contributions**

**Conceptualization:** Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Zelda Stewart, Agnès Dechartres, Catherine Deneux-Tharaux.

**Data curation:** Maxime Eslier, Konstantinos Chatzistergiou, Zelda Stewart.

**Formal analysis:** Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Agnès Dechartres, Catherine Deneux-Tharaux.

**Investigation:** Maxime Eslier, Elie Azria, Catherine Deneux-Tharaux.

**Methodology:** Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Zelda Stewart, Agnès Dechartres, Catherine Deneux-Tharaux.

**Project administration:** Maxime Eslier.

**Software:** Maxime Eslier, Konstantinos Chatzistergiou, Agnès Dechartres.

**Supervision:** Maxime Eslier, Elie Azria, Agnès Dechartres, Catherine Deneux-Tharaux.

**Validation:** Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Agnès Dechartres, Catherine Deneux-Tharaux.
**Visualization:** Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Zelda Stewart, Agnès Dechartres, Catherine Deneux-Tharaux.

**Writing – original draft:** Maxime Eslier, Elie Azria, Catherine Deneux-Tharaux.

**Writing – review & editing:** Maxime Eslier, Elie Azria, Konstantinos Chatzistergiou, Zelda Stewart, Agnès Dechartres, Catherine Deneux-Tharaux.

## References

1. OECD/EU. Settling In 2018: Indicators of Immigrant Integration. Brussels: OECD Publishing, Paris/ European Union [Internet]. 2018 [cited 2023 Apr 19]. https://doi.org/10.1787/9789264307216-en

2. Immigration by age and sex (migr_imm8). [Internet]. [cited 2023 Apr 19]. Available from: https://ec.europa.eu/eurostat/data/database.

3. Abubakar I, Aldridge RW, Devakumar D, Orcutt M, Burns R, Barreto ML, et al. The UCL-Lancet Commission on Migration and Health: the health of a world on the move. Lancet. 2018; 392(10164):2606–2654. https://doi.org/10.1016/S0140-6736(18)32114-7 PMID: 30528486

4. Live births by mother's age and country of birth (demo_facbc). [Internet]. [cited 2023 Apr 19]. Available from: http://ec.europa.eu/eurostat/data/database.

5. Eslier M, Deneux-Tharaux C, Sauvegrain P, Schmitz T, Luton D, Mandelbrot L, et al. Association between Migrant Women's Legal Status and Prenatal Care Utilization in the PreCARE Cohort. Int J Environ Res Public Health. 2020; 17(19):7174. https://doi.org/10.3390/ijerph17197174 PMID: 33007972

6. World report on the health of refugees and migrants. Geneva: World Health Organization; 2022. Licence: CC BY-NC-SA 3.0 IGO.

7. The Lancet Global Health. Refugees and migrants: overexposed yet unseen. Lancet Glob Health. 2022; 10:e1209. https://doi.org/10.1016/S2214-109X(22)00329-1 PMID: 35961328

8. Pedersen GS, Grøntved A, Mortensen LH, Andersen A-MN, Rich-Edwards J. Maternal Mortality Among Migrants in Western Europe: A Meta-Analysis. Matern Child Health J. 2014; 18:1628–1638. https://doi.org/10.1007/s10995-013-1403-x PMID: 24337813

9. Zwart J, Richters J, Öry F, de Vries J, Bloemenkamp K, van Roosmalen J. Severe maternal morbidity during pregnancy, delivery and puerperium in the Netherlands: a nationwide population-based study of 371 000 pregnancies. BJOG. 2008; 115:842–850. https://doi.org/10.1111/j.1471-0528.2008.01713.x PMID: 18485162

10. Saurel-Cubizolles M-J, Saucedo M, Drewniak N, Blondel B, Bouvier-Colle M-H. [Perinatal health of foreign women in France]. Bull Épidémiologique Hebd. 2012; 2:30–34.

11. Van den Akker T, van Roosmalen J. Maternal mortality and severe morbidity in a migration perspective. Best Pract Res Clin Obstet Gynaecol. 2016; 32:26–38. https://doi.org/10.1016/j.bpobgyn.2015.08.016 PMID: 26427550

12. Almeida LM, Santos CC, Caldas JP, Ayres-de-Campos D, Dias S. Obstetric care in a migrant population with free access to health care. Int J Gynaecol Obstet Off Organ Int Fed Gynaecol Obstet. 2014; 126:244–247.

13. Sauvegrain P, Azria E, Chiesa-Dubruille C, Deneux-Tharaux C. Exploring the hypothesis of differential care for African immigrant and native women in France with hypertensive disorders during pregnancy: a qualitative study. BJOG. 2017; 124:1858–1865. https://doi.org/10.1111/1471-0528.14658 PMID: 28342231

14. Singh GK. Trends and Social Inequalities in Maternal Mortality in the United States, 1969–2018. Int J MCH AIDS. 2020; 10:29–42. https://doi.org/10.21106/ijma.444 PMID: 33442490

15. Urquia ML, Wanigaratne S, Ray JG, Joseph KS. Severe Maternal Morbidity Associated With Maternal Birthplace: A Population-Based Register Study. J Obstet Gynaecol Can. 2017; 39:978–987. https://doi.org/10.1016/j.jogc.2017.05.012 PMID: 28733065

16. Creanga AA, Berg CJ, Syverson C, Seed K, Bruce FC, Callaghan WM. Race, ethnicity, and nativity differentials in pregnancy-related mortality in the United States: 1993–2006. Obstet Gynecol. 2012; 120:261–268. https://doi.org/10.1097/AOG.0b013e31825cb87a PMID: 22825083

17. Mujahid MS, Kan P, Leonard SA, Hailu EM, Wall-Wieler E, Abrams B, et al. Birth hospital and racial and ethnic differences in severe maternal morbidity in the state of California. Am J Obstet Gynecol. 2021; 224:219.e1–219.e15. https://doi.org/10.1016/j.ajog.2020.08.017 PMID: 32798461
18. Howell EA, Egorova NN, Janevic T, Balbierz A, Zeitlin J, Hebert PL. Severe Maternal Morbidity Among Hispanic Women in New York City: Investigation of Health Disparities. Obstet Gynecol. 2017; 129:285–294. https://doi.org/10.1097/AOG.0000000000001864 PMID: 28079772

19. Al-Rubaie ZTA, Malcolm Hudson H, Jenkins G, Mahmoud I, Ray JG, Askie LM, et al. The association between ethnicity and pre-eclampsia in Australia: A multicentre retrospective cohort study. Aust N Z J Obstet Gynaecol. 2020; 60:396–404. https://doi.org/10.1111/ajo.13069 PMID: 31583696

20. Salim R, Mfra A, Garmi G, Shalev E. Comparison of intrapartum outcome among immigrant women from Ethiopia and the general obstetric population in Israel. Int J Gynaecol Obstet. 2012; 118:161–165. https://doi.org/10.1016/j.ijgo.2012.02.018 PMID: 22608024

21. Fasanya HO, Hsiao CJ, Armstrong-Sylvester KR, Beal SG. A Critical Review on the Use of Race in Understanding Racial Disparities in Preeclampsia. J Appl Lab Med. 2021; 6:247–256. https://doi.org/10.1093/jalm/jfaa149 PMID: 33227139

22. Knupp RJ, Yuanfan Y, Szychowski JM, Battarbee AN, Subramaniam A. 234 Adverse maternal and neonatal outcomes in latinas compared to Non-Latinx black and Non-Latinx white women. Am J Obstet Gynecol. 2021; 224:S154–S155.

23. Knight M, Kurinczuk JJ, Spark P, Brocklehurst P. Inequalities in maternal health: national cohort study of ethnic variation in severe maternal morbidities. BMJ [Internet]. 2009 [cited 2023 Apr 19]; 338. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2654771/. https://doi.org/10.1136/bmj.b542 PMID: 19261591

24. Donati S, Senatore S, Ronconi A, Regional Maternal Mortality Working Group. Obstetric near-miss cases among women admitted to intensive care units in Italy. Acta Obstet Gynecol Scand. 2012; 91:452–7.

25. Bollini P, Wanner P, Pampallona S. Trends in maternal mortality in Switzerland among Swiss and foreign nationals, 1969–2006. Int J Public Health. 2011; 56:515–521. https://doi.org/10.1007/s00038-010-0213-9 PMID: 21052770

26. Armbrust R, von Rennenberg R, David M. A Retrospective Perinatal Data Analysis of Immigrant and German Women from Representative Birth Cohorts at the Virchow Hospital, Berlin. Geburtshilfe Frauenheilkd. 2016; 76:1157–1162. https://doi.org/10.1055/s-0042-111011 PMID: 27904165

27. Hanprasertpong T, Hanprasertpong J. Pregnancy outcomes in Southeast Asian migrant workers at Southern Thailand. J Obstet Gynaecol. 2015; 35:565–569. https://doi.org/10.3109/01443615.2014.987113 PMID: 25496499

28. Esscher A, Haglund B, Högberg U, Essén B. Excess mortality in women of reproductive age from low-income countries: a Swedish national register study. Eur J Public Health. 2013; 23:274–279. https://doi.org/10.1093/eurpub/cks101 PMID: 22850186

29. Deneux-Tharaux C, Saucedo M. [Epidemiology of maternal mortality in France, 2010–2012]. Gynecol Obstet Fertil Senol. 2017; 45:S8–S21.

30. Luque Fernández MÁ, Gutiérrez Garitano I, Cavanillas AB. Increased risk of maternal deaths associated with foreign origin in Spain: a population based case-control study. Eur J Public Health. 2011; 21:292–294. https://doi.org/10.1093/eurpub/ckp245 PMID: 20570961

31. Eslier M, Morello R, Azria E, Dreyfus M. Comparative study of changes in maternal and perinatal morbidity inequalities among migrant and native women over time, between 2008 and 2014 in France. Eur J Obstet Gynecol Reprod Biol. 2020; 253:76–82. https://doi.org/10.1016/j.ejogrb.2020.07.047 PMID: 32810709

32. Schutte JM, Steegers EAP, Schuitemaker NWE, Santema JG, Boer K de, Pel M, et al. Rise in maternal mortality in the Netherlands. BJOG. 2010; 117:399–406. https://doi.org/10.1111/j.1471-0528.2009.02382.x PMID: 19943828

33. Zanconato G, Cavaliere E, Iacovella C, Vassanelli A, Schweiger V, Cipriani S, et al. Severe maternal morbidity in a tertiary care centre of northern Italy: a 5-year review. J Matern Fetal Neonatal Med. 2012; 25:1025–1028. https://doi.org/10.3109/14767058.2011.614655 PMID: 21854133

34. Garcia-Tizon Larroca S, Arevalo-Serrano J, Duran Vila A, Pintado Recarte MP, Cueto Hernandez I, Solis Pierna A, et al. Human Development Index (HDI) of the maternal country of origin as a predictor of perinatal outcomes—a longitudinal study conducted in Spain. BMC Pregnancy Childbirth. 2017; 17:314. https://doi.org/10.1186/s12884-017-1515-1 PMID: 28934940

35. Gieles NC, Tankink JB, van Midde M, Düker J, van der Lans P, Wessels CM, et al. Maternal and perinatal outcomes of asylum seekers and undocumented migrants in Europe: a systematic review. Eur J Public Health. 2019; 29:714–723. https://doi.org/10.1093/eurpub/ckz042 PMID: 31098629

36. Gagnon AJ, Zimbeck M, Zeitlin J. Migration and perinatal health surveillance: An international Delphi survey. Eur J Obstet Gynecol Reprod Biol. 2010; 149:37–43 https://doi.org/10.1016/j.ejogrb.2009.12.002 PMID: 20074849
37. Leonard SA, Main EK, Lyell DJ, Carmichael SL, Kennedy CJ, Johnson C, et al. Obstetric comorbidity scores and disparities in severe maternal morbidity across marginalized groups. Am J Obstet Gynecol MFM. 2022; 4:100530. https://doi.org/10.1016/j.ajogmf.2021.100530 PMID: 34798329

38. Medcalf KE, Park AL, Vermeulen MJ, Ray JG. Maternal Origin and Risk of Neonatal and Maternal ICU Admission. Crit Care Med. 2016; 44:1314-1326. https://doi.org/10.1097/CCM.0000000000001647 PMID: 26977854

39. Urquia M, Glazier R, Gagnon A, Mortensen L, Nybo Andersen A-M, Janevic T, et al. Disparities in pre-eclampsia and eclampsia among immigrant women giving birth in six industrialised countries. BJOG. 2014; 121:1492-1500. https://doi.org/10.1111/1471-0528.12758 PMID: 24758368

40. Urquia ML, Glazier RH, Mortensen L, Nybo-Andersen A-M, Small R, Davey M-A, et al. Severe maternal morbidity associated with maternal birthplace in three high-immigration settings. Eur J Public Health. 2015; 25:620-625. https://doi.org/10.1093/eurpub/cku230 PMID: 25587005

41. Wanigaratne S, Cole DC, Bassil K, Hyman I, Moineddin R, Urquia ML. Contribution of HIV to Maternal Morbidity Among Refugee Women in Canada. Am J Public Health. 2015; 105:2449-2456. https://doi.org/10.2105/AJPH.2015.302886 PMID: 26469648

42. Wall-Wieler E, Bane S, Lee HC, Carmichael SL. Severe maternal morbidity among U.S.- and foreign-born Asian and Pacific Islander women in California. Ann Epidemiol. 2020; 52:60-63.e2. https://doi.org/10.1016/j.annepidem.2020.07.016 PMID: 32795600

43. Chantry AA, Berrut S, Donati S, Gissler M, Goldacre R, Knight M, et al. Monitoring severe acute maternal morbidity across Europe: A feasibility study. Paediatr Perinat Epidemiol. 2020; 34:416-426. https://doi.org/10.1111/ppe.12557 PMID: 31502306

44. Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. 2021; 372:n71. https://doi.org/10.1136/bmj.n71 PMID: 33782057

45. United Nations, Department of Economic and Social Affairs, Population Division. International Migration 2019; 2019. Report No.: ST/ESA/SER.A/438.

46. Zeitlin J, Mohangoo A, Cuttini M. The European Perinatal Health Report: comparing the health and care of pregnant women and newborn babies in Europe. J Epidemiol Community Health. 2009; 63:681-682. https://doi.org/10.1136/jech.2009.087296 PMID: 19679713

47. Say L, Pattinson RC, Gülmezoglu AM. WHO systematic review of maternal morbidity and mortality: the prevalence of severe acute maternal morbidity (near miss). Reprod Health. 2004; 1:3. https://doi.org/10.1186/1742-4755-1-3 PMID: 15357863

48. Stevenson K, Fellmeth G, Edwards S, Calvert C, Bennett P, Campbell OMR, et al. The global burden of perinatal common mental health disorders and substance use among migrant women: a systematic review and meta-analysis. Lancet Public Health. 2023; 8:e203-e216. https://doi.org/10.1016/S2468-2667(22)00342-5 PMID: 36841561

49. Wells G, Shea B, O'Connell D, et al. The Newcastle-Ottawa Scale (NOS) for assessing the quality of nonrandomised studies in meta-analyses. [Internet]. [cited 2023 Apr 19]. Available from: http://www.ohri.ca/programs/clinical_epidemiology/oxford.asp.

50. McPheeters ML, Kripalani S, Peterson NB, Idowu RT, Jerome RN, Potter SA, et al. Closing the quality gap: revisiting the state of the science (vol. 3: quality improvement interventions to address health disparities). Evid ReportTechnology Assess. 2012;1-475. PMID: 24422952

51. Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA. Cochrane Handbook for Systematic Reviews of Interventions version 6.2 (updated February 2021). Cochrane; 2021. Available from www.training.cochrane.org/handbook.

52. Ioannidis JPA, Patsopoulos NA, Evangelou E. Uncertainty in heterogeneity estimates in meta-analyses. BMJ. 2007; 335:914-916. https://doi.org/10.1136/bmj.39343.408449.80 PMID: 17974687

53. Saucedo M, Deneux-Tharaux C, Pour le Comité National d'Experts sur la Mortalité Maternelle. [Maternal Mortality, Frequency, causes, women's profile and preventability of deaths in France, 2013-2015]. Gynecol Obstet Fertil Senol. 2021; 49:9-26.

54. Knight M, Tuffnell D, Kenyon S, Shakespeare J, Gray R, Kurinczuk JJ, editors, on behalf of MBRRACE-UK. Saving Lives, Improving Mothers' Care—Surveillance of maternal deaths in the UK 2011-13 and lessons learned to inform maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2009-13. Oxford: National Perinatal Epidemiology Unit, University of Oxford; 2015.

55. Knight M, Nair M, Tuffnell D, Shakespeare J, Kenyon S, Kurinczuk JJ, editors, on behalf of MBRRACE-UK. Saving Lives, Improving Mothers' Care—Lessons learned to inform maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2013-15. Oxford: National Perinatal Epidemiology Unit, University of Oxford; 2017.
56. Knight M, Bunch K, Tuffnell D, Shakespeare J, Kotnis R, Kenyon S, Kurinczuk JJ, editors, on behalf of MBRRACE-UK. Saving Lives, Improving Mothers' Care—Lessons learned to inform maternity care from the UK and Ireland Confidential Enquiries into Maternal Deaths and Morbidity 2016–18. Oxford: National Perinatal Epidemiology Unit, University of Oxford; 2020.

57. Diguisto C, Saucedo M, Kallianidis A, Bloemenkamp K, Bødker B, Buoncristiano M, et al. Maternal mortality in eight European countries with enhanced surveillance systems: descriptive population based study. BMJ. 2022; 379:e070621. https://doi.org/10.1136/bmj-2022-070621 PMID: 36384872

58. García-Tizón Larroca S, Arévalo-Serrano J, Ruiz Minaya M, Paya Martinez P, Perez Fernandez Pacheco R, Lizarraga Bonelli S, et al. Maternal mortality trends in Spain during the 2000–2018 period: the role of maternal origin. BMC Public Health. 2022; 22:337. https://doi.org/10.1186/s12889-022-12686-z PMID: 35177052

59. Kallianidis AF, Schutte JM, Schuringa LEM, Beenakkers ICM, Bloemenkamp KWM, Braams-Lisman BAM, et al. Confidential enquiry into maternal deaths in the Netherlands, 2006–2018. Acta Obstet Gynecol Scand. 2022; 101:441–449. https://doi.org/10.1111/aogs.14312 PMID: 35352820

60. AIHW: Johnson S, Bonello MR, Li Z, Hilder L, Sullivan EA. Maternal deaths in Australia 2006–2010. Maternal deaths series no. 4. Cat. no. PER 61. Canberra: AIHW.

61. H AIHW: Humphrey MD, Bonello MR, Chughtai A, Macaldowie A, Harris K, Chambers GM 2015. Maternal deaths in Australia 2008–2012. Maternal deaths series no. 5. Cat. no. PER 70. Canberra: AIHW.

62. Australian Institute of Health and Welfare: Humphrey MD et al 2017. Maternal deaths in Australia 2012–2014. Cat. no. PER 92. Canberra: AIHW.

63. Australian Institute of Health and Welfare: Humphrey MD et al 2020. Maternal deaths in Australia 2015–2017. Cat. no. PER 106. Canberra: AIHW.

64. Eslier M, Deneux-Tharaux C, Sauvegrain P, Schmitz T, Luton D, Mandelbrot L, et al. Severe maternal morbidity among undocumented migrant women in the PreCARE prospective cohort study. BJOG. 2022; 129:1762–1771. https://doi.org/10.1111/1471-0528.17124 PMID: 35157345

65. Zwart JJ, Dupuis JRO, Richters A, Ory F, van Roosmalen J. Obstetric intensive care unit admission: a 2-year nationwide population-based cohort study. Intensive Care Med. 2010; 36:256–263. https://doi.org/10.1007/s00134-009-1707-x PMID: 19902177

66. Zwart JJ, Jonkers MD, Richters A, Öry F, Bloemenkamp KW, Duvekot JJ, et al. Ethnic disparity in severe acute maternal morbidity: a nationwide cohort study in the Netherlands. Eur J Public Health. 2011; 21:229–234. https://doi.org/10.1093/eurpub/ckq046 PMID: 20522516

67. Van Hanegem N, Miltenburg AS, Zwart JJ, Bloemenkamp KWM, Van Roosmalen J. Severe acute maternal morbidity in asylum seekers: a two-year nationwide cohort study in the Netherlands: Severe maternal morbidity in asylum seekers. Acta Obstet Gynecol Scand. 2011; 90:1010–1016.

68. Jairam JA, Vigod SN, Siddiqi A, Guan J, Boblitz A, Wang X, et al. Severe Maternal Morbidity and Mortality Among Immigrant and Canadian-Born Women Residing Within Low-Income Neighborhoods in Ontario, Canada JAMA Netw Open. 2023; 6:e2256203.

69. Turner JM, Spink K, Fox J, Kumar SS. Refugee women have significantly poorer perinatal outcomes despite a specialised refugee midwifery service. J Paediatr Child Health. 2020; 56:128–129.

70. Gulersen M, Lenchner E, Grunebaum A, Chervenak FA, Bornstein E. Impact of maternal nativity among maternal racial and ethnic groups at risk for preterm birth. Am J Obstet Gynecol. 2022; 226: S725.

71. David M, Razum O, Henrich W, Ramsauer B, Schlembach D, Breckenkamp J. The impact of migration background on maternal near miss. Arch Gynecol Obstet. 2019; 300:285–292. https://doi.org/10.1007/s00404-019-05179-9 PMID: 31076854

72. Wahlberg Å, Rööst M, Haglund B, Högberg U, Essén B. Increased risk of severe maternal morbidity (near-miss) among immigrant women in Sweden: a population register-based study. BJOG. 2013; 120:1605–1612. https://doi.org/10.1111/1471-0528.12326 PMID: 23786308

73. Reime B, Janssen PA, Farris L, Borde T, Hellmers C, Myezwa H, et al. Maternal near-miss among women with a migrant background in Germany. Acta Obstet Gynecol Scand. 2012; 91:824–829. https://doi.org/10.1111/j.1600-0412.2012.01390.x PMID: 22404729

74. Flood M, Pollock W, McDonald S, Cullinane F, Davey MA. Maternal country of birth and blood transfusion for 370,603 confinements in Victoria. Women Birth. 2019; 32:S14.

75. Sacramento: California Department of Public Health, Maternal, Child and Adolescent Health Division. CA-PMSS Surveillance Report: Pregnancy-Related Deaths in California, 2008–2016. 2021.

76. Hoyert DL. Maternal mortality rates in the United States, 2020. NCHS Health E-Stats. 2022. https://doi.org/10.15620/cdc.113967
77. Gonthier C, Estellat C, Deneux-Tharaux C, Blondel B, Alfaiate T, Schmitz T, et al. Association between maternal social deprivation and prenatal care utilization: the PreCARE cohort study. BMC Pregnancy Childbirth. 2017; 17. https://doi.org/10.1186/s12884-017-1310-z PMID: 28506217

78. Linard M, Blondel B, Estellat C, Deneux-Tharaux C, Luton D, Oury J, et al. Association between inadequate antenatal care utilisation and severe perinatal and maternal morbidity: an analysis in the Pre-CARE cohort. BJOG. 2018; 125:587-595. https://doi.org/10.1111/1471-0528.14794 PMID: 28631308

79. Anselem O, Saurel-Cubizolles MJ, Khoshnood B, Blondel B, Sauvegrain P, Bertille N, et al. Does women's place of birth affect their opportunity for an informed choice about Down syndrome screening? A population-based study in France. BMC Pregnancy Childbirth. 2021; 21:590. https://doi.org/10.1186/s12884-021-04041-8 PMID: 34461849

80. Linard M, Deneux-Tharaux C, Luton D, Schmitz T, Mandelbrot L, Estellat C, et al. Differential rates of cesarean delivery by maternal geographical origin: a cohort study in France. BMC Pregnancy Childbirth. 2019; 19:217. https://doi.org/10.1186/s12884-019-2364-x PMID: 31248386

81. Azria E, Sauvegrain P, Anselem O, Bonnet MP, Deneux-Tharaux C, Rousseau A, et al. Implicit biases and differential perinatal care for migrant women: Methodological framework and study protocol of the BiP study part 3. J Gynecol Obstet Hum Reprod. 2022; 51:102340.

82. Payne BK, Hannay JW. Implicit bias reflects systemic racism. Trends Cogn Sci. 2021; 25:927-936. https://doi.org/10.1016/j.tics.2021.08.001 PMID: 34426051

83. Evans MK, Rosenbaum L, Malina D, Morrissey S, Rubin EJ. Diagnosing and Treating Systemic Racism. N Engl J Med. 2020; 383:274-276. https://doi.org/10.1056/NEJMe2021693 PMID: 32521155

84. McAuliffe M, Triandafyllidou A. World Migration Report 2022. Geneva: International Organization for Migration (IOM); 2021.