Title: Associations between domestic violence and poor pregnancy outcomes in Taiwanese
women: A nested case–control study
Version: 1 Date: 27 May 2023
Reviewer's report:
1. The study design of this research only mentions the use of a "nested case-control study"
without providing a clear explanation. It is recommended that the text should have a clearer
description of the data extraction process instead of relying on Figure 1 for readers to imagine
on their own, especially considering that Figure 1 contains errors.
(1) The matching criteria stated in Figure 1, "3.4-fold propensity score matching by gender,
age, and index date," are incorrect. Since this study focuses on pregnant women, the variable of
"gender" should not be included. Additionally, "age" should be corrected to "age group," and
"index date" should be modified to "index year." Furthermore, it should be further explained
that "index year" refers to the year of delivery.
(2) There is inconsistency between the flowchart in Figure 1 and the numbers in Tables 2 and
3. In Figure 1, the arrow pointing downward from the control group indicates "prior exposure
to violence" for 102 individuals. However, Tables 2 and 3 state that there are 102 individuals
in the "without violence" group.
2. Domestic violence (DV) is the most important independent variable in this study, so it is
crucial to accurately capture DV. The study uses NHIRD for research analysis and relies solely
on ICD-9-CM codes for identification. However, it is possible that the estimation may be
underestimated if individuals do not seek medical help due to stigma, trauma, or safety concerns.
In the introduction, the authors mention, "Based on the Ministry of Health and Welfare of
Taiwan's reports, the prevalence of DV was 8.99% in Taiwan in 2021 and increased by year."
Although this official statistical figure does not specify the surveyed population, it significantly
differs from the numbers extracted in this study. It is recommended that the authors attempt
to find other official statistical data or previous research data specifically related to "domestic
violence among women of childbearing age" to compare with the figures in this study for
stronger support.
3. Building upon point 2, since the data extraction period spans from 2000 to 2015, DV could
have occurred at any time within these 16 years. Would DV that occurred 10 years ago have an
impact on PPOs 10 years later? The intensity and frequency of DV are the core issues, but these
important pieces of information cannot be obtained from the data in this study. Therefore, it
poses a significant limitation to the research (although the authors mentioned it in the limitations
section, it remains a major concern).
4. The article mentions that all variables (DV, PPOs, comorbidities, etc.) were extracted using
ICD-9-CM, but it does not explain how the extraction criteria were set. Did it consider only
the primary diagnosis or also the secondary diagnoses? Within what timeframe and how many
occurrences of diagnostic codes were considered to indicate the presence of a specific condition
or disease?
5. There are many indicators for adverse pregnancy outcomes, so please explain why this study
chose premature delivery, abortion, and stillbirth as PPOs.
6. How was "parity" extracted? Is it possible to obtain the childbirth records prior to 2000? If it
is not possible to obtain them, how can we ensure the accuracy of parity?
7. Building upon point 6, is it possible that pregnant women with parity of 2 or more experienced
PPOs due to advanced maternal age during their second (or third) pregnancy, rather than as a
result of DV?
8. From Table 1, it can be observed that the case group (PPOs) has significantly more severe
comorbidities compared to the control group. Therefore, the PPOs in the case group could also
be attributed to the severity of comorbidities rather than solely caused by DV. The subsequent
analyses in this study did not control or adjust for variables such as disease severity.
9. In the Results section, under 3.1 Demographic data, the second line states, "with a mean age
of 35.53±19.17 years, and compared with the controls." However, the results of the comparison
are not mentioned here."
10. 3.1 Factors of PPOs stratified by using conditional logistic regression should be labeled
as "3.2," and "3.2 Factors of PPO subtypes by using conditional logistic regression" should be
labeled as "3.3."
11. Why are the person-years (PYs) the same for all three PPOs (premature delivery, abortion,
and stillbirth) in Table 3?
12. In the paragraph "3.1 Factors of PPOs stratified by using conditional logistic regression,"
it states, "When the age group was divided, there was a significantly higher risk of PPOs in
subjects aged 45-49 compared with in the other age groups (AOR = 3.70, 95% CI: 3.17-4.32)."
However, there was no statistical testing conducted between the groups, so it should not be
written as "compared with in the other age groups."
13. In the conditional logistic regression in Tables 2 to 4, were any control variables included
for adjustment?