# First-Trimester PlGF and PAPP-A and the Risk of Placenta-Mediated Complications: PREDICTION Prospective Study

Marie-Laurence Côté, Yves Giguère, Jean-Claude Forest, Francois Audibert, Jo Ann Johnson, Nan Okun, Paul Guerby, Louise Ghesquiere, Emmanuel Bujold

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Marie-Laurence Côté, Yves Giguère, Jean-Claude Forest, Francois Audibert, Jo Ann Johnson, et al. First-Trimester PlGF and PAPP-A and the Risk of Placenta-Mediated Complications: PREDICTION Prospective Study. Journal of Obstetrics and Gynaecology Canada = Journal d'obstétrique et gynécologie du Canada, 2025, 47 (2), pp.102732. 10.1016/j.jogc.2024.102732. hal-05039510

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# First-Trimester PIGF and PAPP-A and the Risk of Placenta-Mediated Complications: PREDICTION Prospective Study

Marie-Laurence Côté, MD;<fnref n="1" /> Yves Giguère, MD, PhD;<fnref n="1" />,<fnref n="2" /> Jean-Claude Forest, MD, PhD;<fnref n="1" />,<fnref n="2" />

Francois Audibert, MD, MSc;<fnref n="3" /> Jo Ann Johnson, MD;<fnref n="4" /> Nan Okun, MD;<fnref n="5" /> Paul Guerby, MD, PhD;<fnref n="6" />

Louise Ghesquiere, MD, PhD;<fnref n="7" /> Emmanuel Bujold, MD, MSc<fnref n="1" />,<fnref n="8" />

## ABSTRACT

**Objectives:** This study aimed to estimate the association between low first-trimester maternal serum PIGF (placental growth factor) and PAPP-A (pregnancy-associated plasma protein A) and the risk of placenta-mediated complications.

**Methods:** We performed a secondary analysis of the PREDICTION study, including nulliparous participants recruited at 11 to 14 weeks of pregnancy. First-trimester PIGF and PAPP-A levels were

**Keywords:** pregnancy; preeclampsia; prenatal screening; placenta; placental growth factor (PIGF); pregnancy-associated plasma protein A (PAPP-A)

**Corresponding author:** Emmanuel Bujold,
emmanuel.bujold@crchdequebec.ulaval.ca

**Disclosures:** This study was supported by the Canadian Institutes of Health Research (operating grant #311201), the J.-Louis Lévesque Foundation, and the Jeanne and J.-Louis Levesque Perinatal Research Chair at Université Laval, Québec, Canada. Prof. Emmanuel Bujold holds a Clinician Scientist award from Fonds de recherche du Québec - Santé (FRQS), Québec, Canada. Dr. Paul Guerby holds a postdoctoral award from the FRQS and INSERM (Institut National de la Santé et de la Recherche Médicale). Dr. Louise Ghesquiere holds a postdoctoral award from the Fondation de l'Université Laval. An unrestricted grant was obtained from Thermo Fisher - BRAHMS that provided the reagents and kits to measure the biochemical markers.

Each author has indicated they meet the journal's requirements for authorship.

Received on September 16, 2024

Accepted on November 5, 2024

Available online December 2, 2024

reported in multiples of the median (MoM) adjusted for maternal characteristics and gestational age. Participants were stratified into 4 groups based on absence/presence of low (<0.4 MoM) PIGF and PAPP-A values. A composite of adverse pregnancy outcomes (including preeclampsia, fetal growth restriction, fetal death, and placental abruption) was calculated for deliveries occurring before 34 weeks, before 37 weeks, and at or after 37 weeks.

**Results:** Out of the 7262 participants, 86 (1.2%) experienced the composite outcome before 37 weeks of gestation, including 35 (0.4%) before 34 weeks. The combination of low PAPP-A and low PIGF levels was associated with the greatest risk of adverse outcomes before 37 weeks (21%) and before 34 weeks (12%) compared with low PIGF alone (7% and 3%), low PAPP-A alone (2% and 1%), or neither marker (1% and 0.4%, respectively; *P* < 0.001). For preterm preeclampsia specifically, the combination of low PAPP-A and low PIGF was also associated with a greater risk (12%) compared with low PIGF alone (6%), low PAPP-A alone (0.5%), or neither marker (0.7%; *P* < 0.001).

**Conclusions:** The combination of low PAPP-A and low PIGF levels is associated with a very high risk for adverse outcomes before 34 and 37 weeks. An isolated low PAPP-A should not be considered a risk factor for adverse pregnancy outcomes.

## RÉSUMÉ

**Objectifs :** Estimer l'association entre un faible taux sérique maternel de facteur de croissance placentaire (PIGF) et de protéine A plasmatique associée à la grossesse (PAPP-A) au premier trimestre et le risque de complications à médiation placentaire.

**Méthodes :** Nous avons effectué une analyse secondaire de l'étude PREDICTION en incluant les participantes nullipares recrutées entre 11 et 14 semaines d'aménorrhée (SA). Les taux de PIGF et de PAPP-A du premier trimestre ont été présentés en multiples de

<footnote n="1">¹Reproduction, Mother and Child Health Unit, CHU De Québec-Université Laval Research Center, Université Laval, Québec City, Québec, Canada</footnote>

<footnote n="2">²Department of Molecular Biology, Medical Biochemistry and Pathology, Faculty of Medicine, Université Laval, Québec City, Québec, Canada</footnote>

<footnote n="3">³Department of Obstetrics and Gynecology, CHU Sainte-Justine, Université de Montréal, Montréal, Québec, Canada</footnote>

<footnote n="4">⁴Department of Obstetrics and Gynaecology, University of Calgary, Calgary, Alberta, Canada</footnote>

<footnote n="5">⁵Department of Obstetrics and Gynaecology, University of Toronto, Toronto, Ontario, Canada</footnote>

<footnote n="6">⁶Department of Gynecology and Obstetrics, Infinity CNRS, Inserm UMR 1291, CHU Toulouse, Toulouse, France</footnote>

<footnote n="7">⁷Department of Obstetrics and Gynecology, Université de Lille, Lille, France</footnote>

<footnote n="8">⁸Department of Obstetrics and Gynecology, Faculty of Medicine, Université Laval, Québec City, Québec, Canada</footnote>
la médiane (MoM) ajustés en fonction des caractéristiques maternelles et de l'âge gestationnel. Les participantes ont été réparties en quatre groupes en fonction de l'absence ou de la présence de faibles valeurs de PIGF et de PAPP-A (< 0,4 MoM). Une issue de grossesse défavorable composite (prééclampsie, retard de croissance intra-utérin, mort fœtale et hématome rétroplacentaire) a été calculée pour l'accouchement avant 34 SA, avant 37 SA, et à 37 SA ou plus.

**Résultats** : Des 7262 participantes, 86 (1,2 %) ont développé l'issue composite avant 37 SA, dont 35 (0,4 %) avant 34 SA. La combinaison de faibles taux de PAPP-A et de PIGF a été associée au plus grand risque d'issues défavorables avant 37 SA (21 %) et avant 34 SA (12 %) par rapport à un faible taux de PIGF seul (7 % et 3 %), à un faible taux de PAPP-A seul (2 % et 1 %) ou à l'absence des deux marqueurs (1 % et 0,4 %, respectivement; *P* < 0,001). Si l'on considère spécifiquement la prééclampsie avant terme, la combinaison d'un faible taux de PAPP-A et d'un faible taux de PIGF a également été associée à une augmentation du risque de pré-éclampsie (12 %) par rapport à un faible taux de PIGF (6 %), à un faible taux de PAPP-A (0,5 %) ou à l'absence des deux marqueurs (0,7 %; *P* < 0,001).

**Conclusion** : La combinaison de faibles taux de PAPP-A et de PIGF est associée à un risque très élevé d'issues défavorables avant 34 et 37 SA. Un faible taux de PAPP-A isolé ne doit pas être considéré comme un facteur de risque d'issue de grossesse défavorable.

© 2024 The Author. Published by ELSEVIER INC. on behalf of The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

J Obstet Gynaecol Can 2025;47(2):102732

https://doi.org/10.1016/j.jogc.2024.102732

## INTRODUCTION

Preeclampsia affects approximately 3% to 5% of pregnancies and is a significant cause of maternal and neonatal morbidity and mortality.¹ The exact pathogenesis of preeclampsia is not yet fully understood, but in many cases, impaired remodelling of spiral arteries is implicated, mainly in the cases that occur before 37 weeks gestation.² This impaired remodelling, also reported as a deep placentation disorder, results in reduced placental perfusion and high-velocity and turbulent blood flow, causing placental ischemia and oxidative stress, which in turn damages placental villi and alters angiogenic protein levels in maternal blood.¹ Deep placentation disorders can also lead to other complications of pregnancy, such as fetal growth restriction (FGR), fetal death, placental abruption, and even spontaneous preterm birth.³⁻⁵ The only definitive treatment for preeclampsia is delivery of the placenta.

However, in recent years, the use of aspirin initiated before 16 weeks gestation has been shown to significantly reduce the risk of preeclampsia, mainly the preterm forms of the

disease.⁶,⁷ Rolnik et al. demonstrated that 62% of pre-eclampsia cases requiring delivery before 37 weeks gestation and up to 80% of preeclampsia cases requiring delivery before 34 weeks could be prevented with 150 mg of daily aspirin, with even greater reductions when medication adherence was adequate.⁸ Aspirin initiated before 16 weeks gestation was also associated with a significant reduction of FGR, perinatal death, and even preterm birth, suggesting that its mechanism of action is probably related to a reduction of the deep placentation disorder's effect.⁹,¹⁰ Given the wide availability of an effective prophylaxis, it is crucial to accurately identify patients who could benefit from it.

The Society of Obstetricians and Gynaecologists of Canada (SOGC) has recently recommended that women with 1 clinical high-risk factor or 2 moderate-risk factors take 80–160 mg of aspirin daily to reduce the risk of preeclampsia.¹¹ However, it has been demonstrated that (1) the uptake is slow and remains low; (2) there is a dose-response effect, and 80 mg of aspirin daily is not efficient in reducing the risk of preterm preeclampsia; and more recently, (3) that the method of screening through clinical high-risk and moderate-risk factors would fail to predict most cases of preterm preeclampsia.¹²⁻¹⁶ There is therefore an urgent need to turn to alternatives that enable early identification of persons at risk of developing preterm preeclampsia or associated placental disorders.

The Fetal Medicine Foundation (FMF) has developed an algorithm combining maternal characteristics; biophysical markers (BMI and mean arterial blood pressure), maternal serum markers (PAPP-A [pregnancy-associated plasma protein A] and PIGF [placental growth factor]), and mean uterine artery pulsatility index that can all be assessed in 1 visit between 11 and 14 weeks gestation and that could predict most cases of preterm preeclampsia.¹⁷ Several groups, including ours with the PREDICTION multicentre Canadian study, confirmed the effectiveness of the FMF algorithm in identifying about two-thirds of patients at risk of preterm preeclampsia and three-quarters of patients at risk of early-onset preeclampsia.¹⁸ Considering that first-trimester ultrasound combined with maternal blood markers is widely offered across Canada for screening fetal aneuploidies, we have a unique opportunity to expand this specific screening to a more comprehensive screening that could lead to a reduction in several pregnancy complications.¹⁹,²⁰ Therefore, we need to quickly establish strategies to provide access to comprehensive first-trimester screening, including screening for preterm preeclampsia, across Canada. However, while waiting for the development of necessary enabling tools, it has been
proposed to offer alternatives. Since both PAPP-A and PlGF measured in the first trimester are associated with preterm preeclampsia and other placenta-mediated complications, and given that these tests are now universally offered in several provinces, it has been suggested that they could be used independently for screening for placenta-mediated pregnancy complications.²⁰ However, when faced with abnormal biomarker results and without access to a research algorithm such as the one from the FMF, primary antenatal care providers may struggle to assess the significance of these biomarkers in determining the risk of adverse pregnancy outcomes for their patients and adjusting a treatment approach.

In this context, we performed a secondary analysis of the PREDICTION study to estimate the potential benefit of first-trimester maternal serum PAPP-A and PlGF to predict placenta-mediated complications. Until the health care system offers FMF preeclampsia screening or an equivalent, such analysis could provide clinicians with additional information on interpreting the significance of these biomarker values more effectively, thereby improving their ability to estimate the risk of adverse pregnancy outcomes and to provide more precise information to their patients.

## METHODS

We performed a secondary analysis of the PREDICTION study, which included nulliparous participants recruited between 11 and 14 weeks gestation and followed up until delivery, between 2014 and 2020. Women were not eligible if they were taking antihypertensive medication, aspirin, or low-molecular-weight heparin at the time of the recruitment, and were subsequently excluded in cases of lethal fetal anomalies. At the first-trimester visit, a maternal blood sample was collected for the measurement of the serum PAPP-A and PlGF using a B·R·A·H·M·S KRYPTOR analyzer (Thermo Fisher Scientific). The values of PAPP-A and PlGF were entered in the REDCap (Research Electronic Data Capture) database and were reported in multiples of the median (MoM) adjusted for BMI and gestational age. The study was approved by the institutional ethics review board (B14-05-2024). All participants signed an informed consent form, and each centre's ethics committee approved the project.

The medical records of all participants were reviewed by research nurses, who were unaware of the first-trimester biomarkers results, between 3 and 6 months after the expected delivery date. Data collected included pregnancy outcomes such as preeclampsia (per SOGC guidelines),

FGR (defined as birth weight <10th centile), fetal death, and placental abruption confirmed through medical records and placental pathology reports.¹¹ Any cases involving preterm delivery, birth weight <2500 g, or diagnosed preeclampsia underwent further review by an independent maternal-fetal medicine specialist, also blinDED to the first-trimester biomarkers results, to confirm the diagnosis. A composite of placenta-mediated complications—including preeclampsia, FGR, fetal death, and placental abruption (restricted to cases occurring before 37 weeks)—was reported for each participant, categorized by delivery timing: before 34 weeks, before 37 weeks, and at or after 37 weeks. As aspirin is now indicated for women at risk for preterm preeclampsia (associated with delivery before 37 weeks), we also reported the risk of preterm preeclampsia for each subgroup.

We performed receiver operating characteristic (ROC) curve analyses to estimate the sensitivity and specificity of each biomarker for the prediction of preeclampsia and placenta-mediated complications before 37 and before 34 weeks. We reported the predictive value of each biomarker using the area under the curve (AUC) with the 95% CI. Participants were then stratified into 4 groups based on PlGF and PAPP-A values (combination of low PlGF and low PAPP-A, low PlGF alone, low PAPP-A alone, and no low value). On the basis of previous reports, we considered that a value <0.4 MoM should be considered as abnormal.²¹ The rate of preeclampsia and the rate of the composite of adverse pregnancy outcomes were calculated for each group, stratified by delivery timing: before 34 weeks, before 37 weeks, and after 37 weeks. Non-parametric statistical analyses were used to compare the detection rates (DRs), the screen-positive rates, and the positive predictive value (PPV) and negative predictive value (NPV) of screening approaches using biomarkers. Statistical analyses were performed using IBM SPSS Statistics, Version 29.0 (IBM Corp.) and a *P* value <0.05 was considered significant.

## RESULTS

We recruited 7554 participants, including 7325 (97%) who delivered a singleton fetus without lethal anomaly after 20 weeks gestation and with complete follow-up. The reasons for exclusion were congenital fetal anomalies (n = 73), fetal loss before 16 weeks (n = 48), multiple pregnancy (n = 23), voluntary termination of pregnancy (n = 12), and loss to follow-up (n = 73). PlGF and/or PAPP-A was not available for 63 (1%) participants, leaving 7262 (99%) participants eligible for the current secondary analyses.¹⁸ Of note, calcium supplementation (mostly through
<table><caption>Table 1. Characteristics of the participants according to the first-trimester biochemical marker categories</caption><thead><tr><th rowspan="2">Characteristics</th><th colspan="4">First-trimester biochemical markers</th><th rowspan="2">P value</th></tr><tr><th>Low PAPP-A and low PIGF<sup>a</sup><br>n = 34</th><th>Isolated low PIGF<br>n = 109</th><th>Isolated low PAPP-A<br>n = 212</th><th>PAPP-A and PIGF normal<br>n = 6907</th></tr></thead><tbody><tr><td>Maternal age (y)</td><td>29 (27–32)</td><td>30 (27–33)</td><td>29 (27–33)</td><td>29 (27–33)</td><td>NS</td></tr><tr><td>White</td><td>85%</td><td>88%</td><td>90%</td><td>92%</td><td>&lt; 0.01</td></tr><tr><td>BMI (kg/m<sup>2</sup>)</td><td>24 (23–27)</td><td>24 (21–28)</td><td>24 (22–28)</td><td>24 (22–28)</td><td>NS</td></tr><tr><td>In vitro fertilisation</td><td>0</td><td>8 (7%)</td><td>9 (4%)</td><td>201 (3%)</td><td>0.03<sup>b</sup></td></tr><tr><td>Smoking</td><td>0</td><td>0</td><td>14 (7%)</td><td>452 (7%)</td><td>.02</td></tr><tr><td>Prenatal calcium</td><td>29 (85%)</td><td>86 (79%)</td><td>184 (87%)</td><td>5683 (82%)</td><td>NS</td></tr><tr><td>Prenatal aspirin</td><td>2 (6%)</td><td>12 (11%)</td><td>13 (6%)</td><td>305 (4%)</td><td>&lt; 0.01</td></tr><tr><td>Prenatal LMWH</td><td>0</td><td>1 (1%)</td><td>3 (1%)</td><td>49 (1%)</td><td>NS</td></tr><tr><td>GA at sampling (wk)</td><td>13 (12–13)</td><td>13 (12–13)</td><td>13 (12–13)</td><td>13 (12–13)</td><td>NS</td></tr><tr><td>GA at delivery (wk)</td><td>39 (37–40)</td><td>39 (37–40)</td><td>40 (39–41)</td><td>40 (39–41)</td><td>&lt; 0.01</td></tr></tbody></table>

Continuous variables are reported as median (IQR).

GA: gestational age; LMWH: low-molecular-weight heparin; NS: not significant; PAPP-A: pregnancy-associated plasma protein A; PIGF: placental growth factor.

prenatal multivitamins) was reported by 6190 (82%) participants in the first and second trimester of pregnancy. Moreover, 323 (4%) participants reported having taken aspirin at some point during pregnancy, including 157 (2%) who took 80 or 81 mg daily in the periconceptional period in the context of assisted reproductive technology protocols. Furthermore, 53 (1%) participants received low-molecular-weight heparin during pregnancy. Of the 7262 eligible participants, 64 (0.9%) developed preterm preeclampsia, and 86 (1.2%) experienced the composite outcome associated with a delivery before 37 weeks, including 20 (0.2%) cases of preeclampsia and 35 (0.4%) cases of adverse pregnancy outcomes associated with a delivery before 34 weeks. The 86 cases of adverse pregnancy outcomes before 37 weeks included 8 cases of fetal death, 11 cases of isolated FGR, 1 case of isolated

placental abruption, 38 cases of isolated preterm preeclampsia, and 28 cases of >1 adverse outcome in the same participant. PIGF levels <0.4 MoM were observed in 143 (2.0%) participants, and PAPP-A levels <0.4 MoM were observed in 246 (3.4%), including 34 (0.4%) participants who had both markers below the threshold values. Table 1 reports the characteristics of the participants according to each subgroup (both markers abnormal, low PIGF only, low PAPP-A only, and neither of the two). We observed that women with low PIGF levels were less likely to be White, less likely to smoke, more likely to have taken aspirin during pregnancy, and more likely to have undergone in vitro fertilization.

Table 2 reports the AUC of the ROC curves for first-trimester PIGF and PAPP-A levels in the prediction of

<table><caption>Table 2. ROC curve analyses for first-trimester PIGF and PAPP-A levels in the prediction of preterm and early-onset preeclampsia and placenta-mediated complications</caption><thead><tr><th rowspan="2">Outcomes</th><th colspan="6">Area under the ROC curves (95% CI)</th></tr><tr><th>PIGF</th><th>P value</th><th>PAPP-A</th><th>P value</th><th>Difference between AUC</th><th>P value</th></tr></thead><tbody><tr><td>Preeclampsia</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>&lt;37 wk</td><td>0.72 (0.65–0.78)</td><td>&lt;.001</td><td>0.55 (0.47–0.63)</td><td>0.19</td><td>0.17 (0.08–0.26)</td><td>&lt; 0.001</td></tr><tr><td>&lt;34 wk</td><td>0.81 (0.72–0.90)</td><td>&lt;.001</td><td>0.64 (0.52–0.75)</td><td>0.03</td><td>0.17 (0.04–0.31)</td><td>0.01</td></tr><tr><td>Placenta-mediated complication (composite outcome)</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>&lt;37 wk</td><td>0.71 (0.65–0.77)</td><td>&lt;.001</td><td>0.61 (0.54–0.67)</td><td>0.01</td><td>0.11 (0.04–0.18)</td><td>0.003</td></tr><tr><td>&lt;34 wk</td><td>0.77 (0.68–0.85)</td><td>&lt;.001</td><td>0.67 (0.59–0.75)</td><td>0.001</td><td>0.10 (0.005–0.19)</td><td>0.04</td></tr></tbody></table>

AUC: area under the curve; PAPP-A: pregnancy-associated plasma protein A; PIGF: placental growth factor; ROC: receiver operating characteristic.

<footnote><sup>a</sup>Defined as values <0.4 multiples of the median.</footnote>

<footnote><sup>b</sup>Fisher exact test.</footnote>
<table><caption>Table 3. Adverse pregnancy outcomes according to the first-trimester biochemical marker categories</caption><thead><tr><th rowspan="2">Pregnancy outcomes</th><th colspan="4">First-trimester biochemical markers</th><th rowspan="2">P value</th></tr><tr><th>Low PAPP-A and low PIGF<br>n = 34</th><th>Isolated low PIGF<br>n = 109</th><th>Isolated low PAPP-A<br>n = 212</th><th>PAPP-A and PIGF normal<br>n = 6907</th></tr></thead><tbody><tr><td><strong>Preeclampsia</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>&lt;34 wk</td><td>1 (2.9)<sup>a</sup></td><td>3 (2.8)<sup>a</sup></td><td>0 (0)</td><td>17 (0.2)</td><td>&lt; 0.01</td></tr><tr><td>34-36 wk</td><td>3 (8.8)<sup>a</sup></td><td>3 (2.8)<sup>a</sup></td><td>1 (0.5)</td><td>36 (0.5)</td><td>&lt; 0.001</td></tr><tr><td>≥37 wk</td><td>0</td><td>8 (7.5)<sup>a</sup></td><td>6 (2.8)</td><td>170 (2.3)</td><td>&lt; 0.01</td></tr><tr><td><strong>Placenta-mediated complication (composite outcome)</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>&lt;34 wk</td><td>4 (11.8)<sup>a</sup></td><td>3 (2.8)<sup>a</sup></td><td>2 (0.9)</td><td>26 (0.4)</td><td>&lt; 0.01</td></tr><tr><td>34-36 wk</td><td>3 (8.8)<sup>a</sup></td><td>4 (3.8)<sup>a</sup></td><td>3 (1.4)</td><td>41 (0.6)</td><td>&lt; 0.01</td></tr><tr><td>≥37 wk</td><td>7 (20.6)<sup>a</sup></td><td>18 (16.9)<sup>a</sup></td><td>33 (9.4)<sup>a</sup></td><td>383 (5.6)</td><td>&lt; 0.01</td></tr></tbody></table>

Results are reported as number (% or positive predictive value).

PAPP-A: pregnancy-associated plasma protein A; PIGF: placental growth factor.

preeclampsia before 37 weeks and before 34 weeks and placenta-mediated complications before 37 weeks and before 34 weeks. Low PIGF level was associated with preeclampsia before 37 weeks and before 34 weeks and placenta-mediated outcomes before 37 weeks and before 34 weeks. Low PAPP-A was associated with preeclampsia before 34 weeks and placenta-mediated outcomes before 37 and 34 weeks. Comparing the AUC curves, we observed that PIGF was superior to PAPP-A for the prediction of preeclampsia and the composite outcome at all gestational ages.

Table 3 reports the rate (PPV) of preeclampsia and the rate of adverse pregnancy outcomes associated with delivery before 34 weeks, before 37 weeks, and after 37 weeks in each subgroup according to the PIGF and PAPP-A values. We observed significantly increased rates of preeclampsia and adverse pregnancy outcomes at all

gestational ages among women who had a combination of low PAPP-A and low PIGF levels (<0.4 MoM). An isolated low PAPP-A was not associated with greater rates of preterm preeclampsia or preterm adverse pregnancy outcomes when PIGF levels were within the normal range. Across all gestational ages, 12% (4/34) of participants with a combination of low PAPP-A and low PIGF levels had preeclampsia, and 41% (14/34) had an adverse pregnancy outcome. By comparison, 13% (14/109) of participants with isolated low PIGF developed preeclampsia, and 23% (25/109) had adverse pregnancy outcomes; 3% (7/212) of participants with isolated low PAPP-A developed preeclampsia, and 18% (38/212) had adverse pregnancy outcomes; and 3% (223/6907) of participants with normal PAPP-A and PIGF levels developed preeclampsia, and 7% (450/6907) had adverse pregnancy outcomes (P < 0.001).

<table><caption>Table 4. Performance of different approaches of preterm preeclampsia screening</caption><thead><tr><th>Screening approaches</th><th>DR</th><th>FPR</th><th>PPV</th><th>NPV</th></tr></thead><tbody><tr><td>PAPP-A &lt;0.4 MoM (regardless of PIGF)</td><td>8</td><td>3</td><td>2</td><td>&gt;99</td></tr><tr><td>Isolated PAPP-A &lt;0.4 MoM (normal PIGF)</td><td>2</td><td>3</td><td>1</td><td>&gt;99</td></tr><tr><td>PIGF &lt;0.4 MoM (regardless of PAPP-A)</td><td>16</td><td>2</td><td>7</td><td>&gt;99</td></tr><tr><td>Isolated PIGF &lt;0.4 MoM (normal PAPP-A)</td><td>9</td><td>1</td><td>6</td><td>&gt;99</td></tr><tr><td>Combination of low PAPP-A and low PIGF</td><td>6</td><td>&lt;1</td><td>12</td><td>&gt;99</td></tr><tr><td>SOGC screening for preeclampsia</td><td>49</td><td>25</td><td>2</td><td>&gt;99</td></tr><tr><td>FMF algorithm (risk &gt;1/110)</td><td>63</td><td>16</td><td>3<sup>a</sup></td><td>&gt;99</td></tr></tbody></table>

All values are given in %.

DR: detection rate; FMF: Fetal Medicine Foundation; FPR: false-positive rate; MoM: multiple of the median; NPV: negative predictive value; PAPP-A: pregnancy-associated plasma protein A; PIGF: placental growth factor; PPV: positive predictive value; SOGC: Society of Obstetricians and Gynaecologists of Canada.

<footnote><sup>a</sup>P < .05 compared with the controls (PAPP-A and PIGF normal).</footnote>

<footnote><sup>a</sup>This is an average for the overall screening: as the algorithm reports a risk, the PPV depends on the estimated risk calculated with the algorithm.</footnote>
Table 4 reports the PPV, NPV, DR, and screen-positive rates of different screening strategies for preterm preeclampsia and for preterm adverse pregnancy outcomes based on serum markers, the most recent SOGC guideline criteria, or the FMF algorithm. While the combination of both abnormal markers was associated with the highest PPV, the FMF algorithm outperformed the other options in terms of DR (all with *P* < 0.01).

Finally, a posteriori analysis was performed to determine the optimal PlGF threshold for predicting preterm preeclampsia in our population. We evaluated the sensitivity and specificity of different thresholds (0.35, 0.4, 0.5, 0.6, 0.7, and 0.8 MoM). Although the statistical power was insufficient to precisely define the optimal threshold, we observed that a PlGF threshold of <0.6 MoM would have had a sensitivity of 31% for a false-positive rate of 9% in our population.

## DISCUSSION

The main findings are as follows: (1) first-trimester PlGF is superior to first-trimester PAPP-A for the prediction of preterm preeclampsia and preterm adverse placenta-mediated outcomes; (2) the combination of low PAPP-A (<0.4 MoM) and low PlGF (<0.4 MoM) levels is associated with a high risk (PPV >10%) of adverse outcomes (including preeclampsia, FGR, fetal death, and placental abruption) before 34 weeks and a very high risk (PPV >20%) of adverse outcomes before 37 weeks; (3) conversely, isolated low PAPP-A levels or isolated low PlGF levels are associated with a low risk (<1%) of adverse outcome before 34 weeks and a moderate risk (1% and 6%, respectively) of adverse pregnancy outcome before 37 weeks.

Our results are consistent with numerous studies that have shown a link between low first-trimester maternal levels of PlGF or PAPP-A and an increased risk of pregnancy complications including preeclampsia, FGR, and preterm delivery.²²⁻²⁴ Similar to our findings, several studies have found a stronger association between low PlGF levels in the first trimester and an increased risk of adverse obstetrical outcomes, mainly preterm preeclampsia, compared with the weaker association observed with low PAPP-A values.²³ Furthermore, consistent with scientific literature, we observed that abnormal first-trimester biochemical markers are more strongly associated with preterm complications than with term complications.²⁴,²⁵

Other Canadian studies previously reported a greater risk of adverse pregnancy outcomes associated with low

PAPP-A or low PlGF levels.²⁵,²⁶ Melamed et al. reported that low first-trimester levels of PAPP-A and PlGF had the highest DR for a composite of placenta-mediated adverse outcomes compared with first-trimester AFP (alpha-fetoprotein) and free B-hCG (free beta human chorionic gonadotropin). They also noted that individual markers demonstrate low discriminatory and predictive accuracy for these adverse outcomes.²⁶ The added value of our study lies in its evaluation of the specific role of each biomarker in isolation or in combination, which is very important in a clinical context where access to both markers is becoming increasingly common. Notably, we highlighted that a lowered PAPP-A level has a relatively low PPV and should not be considered as a risk factor when PlGF levels are within the normal range. Conversely, a low PlGF level (<0.4 MoM) was shown to have a high PPV, but its clinical usefulness as a unique screening test is limited by a DR of approximately 16%. The use of a threshold value of 0.6 MoM instead of 0.4 MoM significantly improves the DR according to our a posteriori analysis. However, this finding should be validated in an independent cohort.

Our study is limited by the fact that only low-risk nulliparous women were included; therefore, the PPV and NPV could differ among parous or nulliparous women with chronic diseases. However, this limitation also serves as a strength: parous women with a previous adverse pregnancy outcome and nulliparous women with chronic diseases are commonly followed more closely with adapted pregnancy care. Parous women with no previous obstetrical complications are less likely to develop pregnancy complications, leaving nulliparous women without chronic disease as those at significant risk without specific screening or follow-up care.²⁷ Second, our analyses were limited to PAPP-A and PlGF, while other markers (e.g., AFP, B-hCG) that are currently used in aneuploidy screening could also be available to the clinicians. While those 2 markers have been associated with preterm adverse pregnancy outcomes, their usefulness is more controversial.²⁶ Boutin et al. demonstrated the absence of benefit of adding the other markers in a risk calculation algorithm.²⁸ Finally, we must highlight the multiple strengths of our study, which include its prospective design, multicentre recruitment spanning several Canadian provinces, and the fact that patients, health care providers, and researchers were all blinded to research biomarker results. Furthermore, laboratory analyses were performed blind to clinical data, and data collection and validation of adverse outcomes were also performed blind to laboratory data. All these precautions greatly limited the risk of bias.
On the basis of our results, we believe that the combina-
tion of low PAPP-A and low PlGF levels should be
considered a significant risk factor for preterm pre-
eclampsia and preterm adverse pregnancy outcomes.
Because of the very high PPV for both outcomes, women
with a combination of low PAPP-A and low PlGF levels
should be followed closely during pregnancy and should
benefit from aspirin initiated before 16 weeks gestation. As
the PPV for preterm preeclampsia and adverse preterm
outcomes is low, isolated PAPP-A should not influence the
clinical approach, as suggested in previous Canadian
studies.²⁹,³⁰ Concerning isolated low PlGF, our study
suggests that it may be associated with a PPV for preterm
preeclampsia >5%, and in this context, aspirin intake
should be considered. However, additional studies should
be conducted to determine the optimal targets in a
screening strategy. We believe that our results will help
clinicians managing low PlGF and/or low PAPP-A from
first-trimester aneuploidy screening by providing them
with a tool to better estimate patient risk until a more
complete screening system, integrating all useful variables
 matern al weight, maternal height and blood pressure, ul-
trasonic data), is available.

CONCLUSION

Our study demonstrated the potential clinical value of
using first-trimester PAPP-A and PlGF levels for adverse
outcomes prediction, including preterm preeclampsia. A
combination of first-trimester PAPP-A and PlGF levels
<0.4 MoM was associated with a significant risk of pre-
term preeclampsia and other placenta-mediated outcomes,
including preeclampsia, FGR, perinatal death, and
placental abruption, while an isolated low PAPP-A with
normal PlGF level was not. A low PlGF level or the
combination of low PlGF and low PAPP-A levels are both
associated with high PPVs for preterm preeclampsia.
However, the overall DRs remain low (<20%), and
therefore the use of biomarkers alone for prediction of
preterm preeclampsia has a limited clinical usefulness.
Given that first-trimester PlGF and PAPP-A testing is now
available in several Canadian provinces, all efforts should
be made to promptly implement a first-trimester algorithm
incorporating all available parameters (such as maternal
age, BMI, blood pressure, biochemical and ultrasound
markers) for optimal prediction of preterm preeclampsia
and judicious use of aspirin prophylaxis.

ETHICS

This study was approved by the CHU de Québec Ethics
Committee (number B14-05-2024).

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