Quantification of selection bias in studies of risk factors for birth defects among livebirths

Unraveling the Role of Maternal Serum Ferritin Levels in Preterm Delivery: A Comprehensive Review

Preterm delivery remains a critical global health concern, with numerous adverse consequences for both neonate and healthcare systems. Understanding the relationship between maternal ferritin levels, as a marker of iron status, and the risk of preterm birth is the focal point of this comprehensive review. We provide insights into the multifaceted nature of this connection, highlighting factors that influence maternal ferritin levels, including dietary intake, genetic and physiological variations, comorbidities, and iron supplementation. While evidence suggests an association between low maternal ferritin levels and preterm birth, causality remains elusive, necessitating further research with robust study designs. The potential mechanisms linking maternal iron status to preterm birth, such as inflammation, infection, and oxidative stress, are explored, underscoring the need for in-depth investigations. This comprehensive review emphasizes the clinical importance of assessing and monitoring maternal ferritin levels in prenatal care and advocates for public health initiatives to raise awareness and provide targeted interventions, particularly in high-risk populations. As we strive to address these unanswered questions and embark on innovative research directions, the aim is to ultimately enhance our understanding of the complex relationship between maternal iron status and preterm birth, leading to improved maternal and child health outcomes.

Risks of obstructive genitourinary birth defects in relation to trihalomethane and haloacetic acid exposures: expanding disinfection byproduct mixtures analyses using relative potency factors

BACKGROUND

Some disinfection byproducts (DBPs) are teratogens based on toxicological evidence. Conventional use of predominant DBPs as proxies for complex mixtures may result in decreased ability to detect associations in epidemiological studies.

OBJECTIVE

We assessed risks of obstructive genitourinary birth defects (OGDs) in relation to 12 DBP mixtures and 13 individual component DBPs.

METHODS

We designed a nested registry-based case-control study (210 OGD cases; 2100 controls) in Massachusetts towns with complete quarterly 1999-2004 data on four trihalomethanes (THMs) and five haloacetic acids (HAAs). We estimated temporally-weighted average DBP exposures for the first trimester of pregnancy. We estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for OGD in relation to individual DBPs, unweighted mixtures, and weighted mixtures based on THM/HAA relative potency factors (RPF) from animal toxicology data for full-litter resorption, eye defects, and neural tube defects.

RESULTS

We detected elevated aORs for OGDs for the highest of bromodichloromethane (aOR = 1.75; 95% CI: 1.15-2.65), dibromochloromethane (aOR = 1.71; 95% CI: 1.15-2.54), bromodichloroacetic acid (aOR = 1.56; 95%CI: 0.97-2.51), chlorodibromoacetic acid (aOR = 1.97, 95% CI: 1.23-3.15), and tribromoacetic acid (aOR = 1.90; 95%CI: 1.20-3.03). Across unweighted mixture sums, the highest aORs were for the sum of three brominated THMs (aOR = 1.74; 95% CI: 1.15-2.64), the sum of six brominated HAAs (aOR = 1.43; 95% CI: 0.89-2.31), and the sum of nine brominated DBPs (aOR = 1.80; 95% CI: 1.05-3.10). Comparing eight RPF-weighted to unweighted mixtures, the largest aOR differences were for two HAA metrics, which both were higher with RPF weighting; other metrics had reduced or minimally changed ORs in RPF-weighted models.

Bias analyses to investigate the impact of differential participation: Application to a birth defects case-control study

BACKGROUND

Certain associations observed in the National Birth Defects Prevention Study (NBDPS) contrasted with other research or were from areas with mixed findings, including no decrease in odds of spina bifida with periconceptional folic acid supplementation, moderately increased cleft palate odds with ondansetron use and reduced hypospadias odds with maternal smoking.

OBJECTIVES

To investigate the plausibility and extent of differential participation to produce effect estimates observed in NBDPS.

METHODS

We searched the literature for factors related to these exposures and participation and conducted deterministic quantitative bias analyses. We estimated case-control participation and expected exposure prevalence based on internal and external reports, respectively. For the folic acid-spina bifida and ondansetron-cleft palate analyses, we hypothesized the true odds ratio (OR) based on prior studies and quantified the degree of exposure over- (or under-) representation to produce the crude OR (cOR) in NBDPS. For the smoking-hypospadias analysis, we estimated the extent of selection bias needed to nullify the association as well as the maximum potential harmful OR.

RESULTS

Under our assumptions (participation, exposure prevalence, true OR), there was overrepresentation of folic acid use and underrepresentation of ondansetron use and smoking among participants. Folic acid-exposed spina bifida cases would need to have been ≥1.2× more likely to participate than exposed controls to yield the observed null cOR. Ondansetron-exposed cleft palate cases would need to have been 1.6× more likely to participate than exposed controls if the true OR is null. Smoking-exposed hypospadias cases would need to have been ≥1.2 times less likely to participate than exposed controls for the association to falsely appear protective (upper bound of selection bias adjusted smoking-hypospadias OR = 2.02).

CONCLUSIONS

Differential participation could partly explain certain associations observed in NBDPS, but questions remain about why. Potential impacts of other systematic errors (e.g. exposure misclassification) could be informed by additional research.

Trends in survival of children with severe congenital heart defects by gestational age at birth: A population-based study using administrative hospital data for England

BACKGROUND

Children with congenital heart defects (CHD) are twice as likely as their peers to be born preterm (<37 weeks' gestation), yet descriptions of recent trends in long-term survival by gestational age at birth (GA) are lacking.

OBJECTIVES

To quantify changes in survival to age 5 years of children in England with severe CHD by GA.

METHODS

We estimated changes in survival to age five of children with severe CHD and all other children born in England between April 2004 and March 2016, overall and by GA-group using linked hospital and mortality records.

RESULTS

Of 5,953,598 livebirths, 5.7% (339,080 of 5,953,598) were born preterm, 0.35% (20,648 of 5,953,598) died before age five and 3.6 per 1000 (21,291 of 5,953,598) had severe CHD. Adjusting for GA, under-five mortality rates fell at a similar rate between 2004-2008 and 2012-2016 for children with severe CHD (adjusted hazard ratio [HR] 0.79, 95% CI 0.71, 0.88) and all other children (HR 0.78, 95% CI 0.76, 0.81). For children with severe CHD, overall survival to age five increased from 87.5% (95% CI 86.6, 88.4) in 2004-2008 to 89.6% (95% CI 88.9, 90.3) in 2012-2016. There was strong evidence for better survival in the ≥39-week group (90.2%, 95% CI 89.1, 91.2 to 93%, 95% CI 92.4, 93.9), weaker evidence at 24-31 and 37-38 weeks and no evidence at 32-36 weeks. We estimate that 51 deaths (95% CI 24, 77) per year in children with severe CHD were averted in 2012-2016 compared to what would have been the case had 2004-2008 mortality rates persisted.

CONCLUSIONS

Nine out of 10 children with severe CHD in 2012-2016 survived to age five. The small improvement in survival over the study period was driven by increased survival in term children. Most children with severe CHD are reaching school age and may require additional support by schools and healthcare services.

Association between First Trimester Exposure to Ambient PM2.5 and NO2 and Congenital Heart Defects: A Population-Based Cohort Study of 1,342,198 Live Births in Canada

BACKGROUND

The extent to which ambient air pollution contributes to the pathogenesis of congenital heart defects remains uncertain.

OBJECTIVE

We investigated whether first trimester exposure to ambient fine particulate matter (PM2.5) and nitrogen dioxide (NO2) was associated with the risk of critical and noncritical heart defects in a large population-based cohort of births.

METHODS

We carried out a retrospective cohort study of children conceived between 2000 and 2016 in Quebec, Canada. Heart defects were identified via data from the Maintenance and Use of Data for the Study of Hospital Clientele registry. The main exposures were average concentration of PM2.5 and NO2 in a) the first trimester and b) the month of conception. Exposures were estimated at the residential postal code. Associations with critical and noncritical heart defects were assessed using logistic regression models, adjusted for maternal and infant characteristics. We considered single- and two-pollutant models and assessed modifying effects of maternal comorbidity, including preexisting hypertension, preeclampsia, anemia, and diabetes.

RESULTS

The cohort comprised 1,342,198 newborns, including 12,715 with heart defects. Exposure in the first trimester and month of conception yielded similar results; both were associated with a greater risk of heart defects. Adjusted odds ratios (OR) for any heart defect per interquartile range increase were 1.02 (95% CI: 1.00, 1.05) for PM2.5 and 1.10 (95% CI: 1.07, 1.13) for NO2. Associations with atrial septal defects were 1.08 (95% CI: 1.03, 1.14) for PM2.5 and 1.19 (95% CI: 1.12, 1.25) for NO2. Corresponding ORs for ventricular septal defects and individual critical heart defects were not significant. PM2.5 (OR=1.11; 95% CI: 1.06, 1.17) and NO2 (OR=1.23; 95% CI: 1.17, 1.31) exposure were associated with a greater risk of heart defects in mothers with comorbidity.

DISCUSSION

In this population-based cohort, prenatal exposure to ambient air pollution during the first trimester was associated with an increased risk of heart defects, particularly atrial septal defects. The association with heart defects was greater in mothers with comorbidity. https://doi.org/10.1289/EHP11120.

Interplay of gestational parent exposure to ambient air pollution and diet characteristics on preterm birth

BACKGROUND

Despite many efforts, preterm birth (PTB) is poorly understood and remains a major public health problem in the United States. Toxicological work suggests gestational parent (GP) diet may modify the effect of ambient pollutants on birth outcomes. We assessed risk of PTB in humans in relation to fine particulate matter (PM2.5), ozone (O3), and nitrogen dioxide (NO2) and variation by diet.

METHODS

684 GP-singleton infant pairs in the Newborn Epigenetics Study prospective birth cohort were attributed ambient air pollutant exposures for each trimester based on residence. Total energy intake, percent of energy intake from saturated fat, and percent of energy intake from total fat were dichotomized at the 75th percentile. >We used log binomial regressions to estimate risk ratios (RR (95%CI)) for PTB by pollutant interquartile ranges, adjusting for GP age, pre-pregnancy body mass index, GP race/ethnicity, GP education, season of conception, household income, and each diet factor. We assessed departure from additivity using interaction contrast ratios (ICRs). We addressed missing covariate data with multiple imputation.

RESULTS

Point estimates suggest that O3 may be inversely associated with PTB when exposure occurs in trimester 2 (min RR: 0.77, 95% CI: 0.39, 1.49), but may be harmful when exposure occurs in trimester 3 (max RR: 1.51, 95% CI: 0.62, 3.64). Additionally, PM2.5 may be inversely associated with PTB when considered with total fat and saturated fat in trimester 2. Imprecise ICRs suggest departure from additivity (evidence of modification) with some pollutant-diet combinations.

CONCLUSIONS

While confidence intervals are wide, we observed potential modification of pollutant associations by dietary factors. It is imperative that large cohorts collect the required data to examine this topic, as more power is necessary to investigate the nuances suggested by this work.

Associations between severe and notifiable respiratory infections during the first trimester of pregnancy and congenital anomalies at birth: a register-based cohort study

BACKGROUND

Evidence regarding the association between acute respiratory infections during pregnancy and congenital anomalies in babies, is limited and conflicting. The aim of this study was to examine the association between acute respiratory infections during the first trimester of pregnancy and congenital anomalies in babies using record linkage.

METHODS

We linked a perinatal register to hospitalisation and disease notifications in the Australian state of New South Wales (NSW) between 2001 to 2016. We quantified the risk of congenital anomalies, identified from the babies' linked hospital record in relation to notifiable respiratory and other infections during pregnancy using generalized Estimating Equations (GEE) adjusted for maternal sociodemographic and other characteristics.

RESULTS

Of 1,453,037 birth records identified from the perinatal register between 2001 and 2016, 11,710 (0.81%) mothers were hospitalised for acute respiratory infection, 2850 (0.20%) had influenza and 1011 (0.07%) had high risk infections (a record of cytomegalovirus, rubella, herpes simplex, herpes zoster, toxoplasmosis, syphilis, chickenpox (varicella) and zika) during the pregnancy. During the first trimester, acute respiratory infection, influenza and high-risk infections were reported by 1547 (0.11%), 399 (0.03%) and 129 (0.01%) mothers. There were 15,644 (1.08%) babies reported with major congenital anomalies, 2242 (0.15%) with cleft lip/ plate, 7770 (0.53%) with all major cardiovascular anomalies and 1746 (0.12%) with selected major cardiovascular anomalies. The rate of selected major cardiovascular anomalies was significantly higher if the mother had an acute respiratory infection during the first trimester of pregnancy (AOR 3.64, 95% CI 1.73 to 7.66). The rates of all major congenital anomalies and all major cardiovascular anomalies were also higher if the mother had an acute respiratory infection during the first trimester of pregnancy, however the difference was no statistically significant. Influenza during the first trimester was not associated with major congenital anomalies, selected major cardiovascular anomalies or all major cardiovascular anomalies in this study.

CONCLUSION

This large population-based study found severe acute respiratory infection in first trimester of pregnancy was associated with a higher risk of selected major cardiovascular anomalies in babies. These findings support measures to prevent acute respiratory infections in pregnant women including through vaccination.

A novel approach to joint prediction of preeclampsia and delivery timing using semicompeting risks

BACKGROUND

Preeclampsia is a pregnancy complication that contributes substantially to perinatal morbidity and mortality worldwide. Existing approaches to modeling and prediction of preeclampsia typically focus either on predicting preeclampsia risk alone, or on the timing of delivery following a diagnosis of preeclampsia. As such, they are misaligned with typical healthcare interactions during which the 2 events are generally considered simultaneously.

OBJECTIVE

This study aimed to describe the "semicompeting risks" framework as an innovative approach for jointly modeling the risk and timing of preeclampsia and the timing of delivery simultaneously. Through this approach, one can obtain, at any point during the pregnancy, clinically relevant summaries of an individual's predicted outcome trajectories in 4 risk categories: not developing preeclampsia and not having delivered, not developing preeclampsia but having delivered because of other causes, developing preeclampsia but not having delivered, and developing preeclampsia and having delivered.

STUDY DESIGN

To illustrate the semicompeting risks methodology, we presented an example analysis of a pregnancy cohort from the electronic health record of an urban, academic medical center in Boston, Massachusetts (n=9161 pregnancies). We fit an illness-death model with proportional-hazards regression specifications describing 3 hazards for timings of preeclampsia, delivery in the absence of preeclampsia, and delivery following preeclampsia diagnosis.

RESULTS

The results indicated nuanced relationships between a variety of risk factors and the timings of preeclampsia diagnosis and delivery, including maternal age, race/ethnicity, parity, body mass index, diabetes mellitus, chronic hypertension, cigarette use, and proteinuria at 20 weeks' gestation. Sample predictions for a diverse set of individuals highlighted differences in projected outcome trajectories with regard to preeclampsia risk and timing, and timing of delivery either before or after preeclampsia diagnosis.

CONCLUSION

The semicompeting risks framework enables characterization of the joint risk and timing of preeclampsia and delivery, providing enhanced, meaningful information regarding clinical decision-making throughout the pregnancy.

The quality and the accuracy of codes for terminations of pregnancy for fetal anomalies recorded in hospital databases in three countries in northern Europe

BACKGROUND

The number of terminations of pregnancy for fetal anomalies in Europe (TOPFA) has increased over recent decades. Therefore, it is important that TOPFAs, in addition to all other birth outcomes, are included in the surveillance of congenital anomalies and in studies on possible teratogenic risks of pregnancy exposures. The aim of this study was to evaluate the quality and the accuracy of codes identifying TOPFA cases in hospital databases.

METHODS

TOPFA cases recorded in three EUROCAT congenital anomaly registries (Finland, 2010-2014; Funen in Denmark, 2005-2014; and northern Netherlands, 2013-2014) were linked to hospital databases using maternal IDs.

RESULTS

A total of 2,114 TOPFA cases over the study period were identified in the registries and 2,096 (99%) of these pregnancies were identified in the hospital databases. An end of pregnancy code was present for 91% of the cases and a code for a congenital anomaly was present for 82% (with some differences across registries). The proportion of TOPFA cases with a code for a specific congenital anomaly was <50% for cases with a structural anomaly (range 0%-50%) and 70% for cases with a chromosomal anomaly.

CONCLUSION

Hospital databases have limited information or codes to identify TOPFAs for specific anomalies and the data are not detailed enough for surveillance of congenital anomalies or for studies analyzing pregnancy exposures and risk of congenital anomalies. However, hospital data may be used to identify the occurrence of a TOPFA to enable more detailed information to be obtained from the medical records.

Prenatal diagnosis and pregnancy outcome of major structural anomalies detectable in the first trimester: A population-based cohort study in the Netherlands

BACKGROUND

Prenatal diagnosis of several major congenital anomalies can be achieved in the first trimester of pregnancy.

OBJECTIVE

This study investigates the timing of diagnosis and pregnancy outcome of foetuses and neonates with selected structural anomalies in the Northern Netherlands over a 10-year period when the prenatal screening programme changed significantly, but no first-trimester anatomical screening was implemented.

METHODS

We performed a population-based retrospective cohort study with data from the EUROCAT Northern Netherlands database on pregnancies with delivery or termination of pregnancy for fetal anomaly (TOPFA) date between 2010 and 2019. The analysis was restricted to anomalies potentially detectable in the first trimester of pregnancy in at least 50% of cases, based on previously published data. These included: anencephaly, encephalocele, spina bifida, holoprosencephaly, tricuspid/pulmonary valve atresia, hypoplastic left heart, abdominal wall and limb reduction defects, lethal skeletal dysplasia, megacystis, multiple congenital anomalies. The primary outcome was the timing of diagnosis of each structural anomaly. Information on additional investigations, genetic testing and pregnancy outcome (live birth, TOPFA and foetal/neonatal death) was also collected.

RESULTS

A total of 478 foetuses were included; 95.0% (n = 454) of anomalies were detected prenatally and 5.0% (n = 24) postpartum. Among the prenatally detected cases, 31% (n = 141) were diagnosed before 14 weeks of gestation, 65.6% (n = 298) between 14-22 weeks and 3.3% (n = 15) after 22 weeks. Prenatal genetic testing was performed in 80.4% (n = 365) of cases with prenatally diagnosed anomalies, and the results were abnormal in 26% (n = 95). Twenty-one% (n = 102) of pregnancies resulted in live births and 62.8% (n = 300) in TOPFA. Spontaneous death occurred in 15.9% (n = 76) of cases: in-utero (6.1%, n = 29), at delivery (7.7%, n = 37) or in neonatal life (2.1%, n = 10).

CONCLUSION

Major structural anomalies amenable to early diagnosis in the first trimester of pregnancy are mostly diagnosed during the second trimester in the absence of a regulated first-trimester anatomical screening programme in the Netherlands and are associated with TOPFA and spontaneous death, especially in cases with underlying genetic anomalies.

Comparing adverse neonatal and maternal outcomes of chlamydia, gonorrhoea, and syphilis infections and co-infections in pregnancy

BACKGROUND

While maternal sexually transmitted infections (STIs) during pregnancy have been extensively studied, fewer studies have directly compared the associations of different infections and co-infections or investigated the association between STIs in pregnancy and maternal outcomes.

OBJECTIVES

We examine associations between STIs and co-infections in pregnancy on risks of adverse neonatal and maternal outcomes.

METHODS

Data from the 2019 US natality files (n = 3,747,882) were used to assess the associations between STIs in pregnancy on adverse pregnancy outcomes. Five mutually exclusive STI groups were examined: a single chlamydia, syphilis, or gonorrhoeal infection, chlamydia and gonorrhoea co-infection, and syphilis co-infection (with chlamydia, gonorrhoea, or both). Demographic and obstetric characteristics among each STI group were compared to those of an uninfected comparison group. Prevalence ratios (PR) of adverse neonatal outcomes (preterm birth, small for gestational age [SGA] births, and 5-min APGAR (Appearance, Pulse, Grimace, Activity, and Respiration) score < 7) and maternal outcomes (gestational hypertension) by STI status were examined using log-binomial regression.

RESULTS

Increased prevalence of preterm birth was apparent, especially among those with a syphilis infection (PR 1.19, 95% confidence intreval [CI] 1.10, 1.30 for single infections and PR 1.31, 95% CI 1.10, 1.57 for co-infections). All STI groups, except gonorrhoea and chlamydia co-infections, were associated with an increased prevalence of gestational hypertension, with the strongest association among those with syphilis co-infections (PR 1.41, 95% CI 1.13, 1.76).

CONCLUSIONS

An increased prevalence was of preterm birth and low APGAR scores were associated with syphilis infection. Increased prevalence of GH among those with STIs warrants further investigation into the relationships and corresponding mechanisms of STIs in pregnancy on adverse maternal outcomes.

Chronic hypertension and risk of preterm delivery: National Longitudinal Study of Adolescents to Adult Health

BACKGROUND

Chronic hypertension during pregnancy is associated with increased risk of adverse birth outcomes. In 2017, the American College of Cardiology and American Heart Association (ACC/AHA) lowered thresholds to classify hypertension in non-pregnant adults to SBP ≥ 130 mmHg and DBP ≥ 80 mmHg (ie stage I hypertension), resulting in an additional 4.5-million reproductive-aged women meeting criteria for hypertension. Little is known about effects of pre-pregnancy blood pressure (BP) in this range.

OBJECTIVES

To examine the effect of pre-pregnancy maternal BP on preterm delivery.

METHODS

We analysed the data from two waves of the National Longitudinal Study of Adolescent to Adult Health, including participants that had measured BP at Wave IV (2008-09) and a pregnancy that resulted in a singleton live birth between Waves IV and V (2016-18; n = 2038). We categorised BP using ACC/AHA cut-offs: normal (SBP < 120 mmHg and DBP < 80 mmHg), elevated (SBP 120-129 mmHg and DBP < 80 mmHg), hypertension stage I (SBP 130-139 mmHg or DBP 80-89 mmHg) and hypertension stage II (SBP ≥ 140 mmHg or DBP ≥ 90 mmHg). We estimated risk ratios (RR) with log-binomial regression adjusting for maternal demographics, anthropometrics and medication use.

RESULTS

The prevalence of preterm delivery was 12.6%. A standard deviation (SD) increment in SBP (SD = 12.2 mmHg) and DBP (SD = 9.3 mmHg) was associated with a 14% (95% confidence interval [CI] 2, 27) and 20% (95% CI 4, 37) higher risk of preterm delivery. Compared to normotensive controls, stage I (RR 1.33, 95% CI 1.01, 1.74) and stage II (RR 1.34, 95% CI 0.89, 2.00) hypertension were associated with increased risk.

CONCLUSIONS

We observed greater risk of preterm delivery among women with higher pre-pregnancy BP. Women with stage I hypertension during pregnancy may benefit from increased BP monitoring. Additional studies on the utility of foetal surveillance in this group are warranted.

Selection bias in multidrug-resistant tuberculosis cohort studies assessing sputum culture conversion

BACKGROUND

Conversion of sputum culture from positive to negative for M. tuberculosis is a key indicator of treatment response. An initial positive culture is a pre-requisite to observe conversion. Consequently, patients with a missing or negative initial culture are excluded from analyses of conversion outcomes. To identify the initial, or "baseline" culture, researchers must define a sample collection interval. An interval extending past treatment initiation can increase sample size but may introduce selection bias because patients without a positive pre-treatment culture must survive and remain in care to have a culture in the post-treatment interval.

METHODS

We used simulated data and data from the endTB observational cohort to investigate the potential for bias when extending baseline culture intervals past treatment initiation. We evaluated bias in the proportion with six-month conversion.

RESULTS

In simulation studies, the potential for bias depended on the proportion of patients missing a pre-treatment culture, proportion with conversion, proportion culture positive at treatment initiation, and proportion of patients missing a pre-treatment culture who would have been observed to be culture positive, had they had a culture. In observational data, the maximum potential for bias when reporting the proportion with conversion reached five percentage points in some sites.

CONCLUSION

Extending the allowable baseline interval past treatment initiation may introduce selection bias. If investigators choose to extend the baseline collection interval past treatment initiation, the proportion missing a pre-treatment culture and the number of deaths and losses to follow up during the post-treatment allowable interval should be clearly enumerated.

Safety of Tenofovir Disoproxil Fumarate for Pregnant Women Facing the Coronavirus Disease 2019 Pandemic

We assessed the teratogenicity of tenofovir, a human immunodeficiency virus (HIV) drug similar to remdesivir that is currently being evaluated for the treatment of coronavirus disease 2019 (COVID-19). Using US Medicaid Analytic eXtract (MAX) claims data (2000-2014), we identified a population-based pregnancy cohort of women with HIV who filled at least 1 prescription for antiretroviral therapies (ART) during the first trimester. Women on tenofovir disoproxil fumarate (TDF) were compared with women receiving ART without TDF. Major malformations were identified by International Classification of Diseases, Ninth Revision, codes using validated algorithms. Relative risks and 95% confidence intervals were estimated using propensity score stratification to control for potential confounders. We incorporated the results into prior knowledge by conducting a systematic literature review and a meta-analysis. Major congenital malformations were diagnosed in 37 out of 866 (4.27%) infants exposed to TDF and 38 out of 1,020 (3.73%) infants exposed to ART other than TDF; the adjusted relative risk was 1.21 (95% confidence interval: 0.77, 1.90). Estimates for specific malformations were imprecise. The pooled relative risk from the meta-analysis with 6 prior studies was 0.88 (95% confidence interval: 0.75, 1.03). Based on evidence accumulated in patients with HIV, first-trimester TDF use does not increase the risk of major congenital malformations overall in the newborn compared with other ART.

Effect of prenatal screening on trends in perinatal mortality associated with congenital anomalies before and after the introduction of prenatal screening: A population-based study in the Northern Netherlands

BACKGROUND

Perinatal mortality in foetuses/children with congenital anomalies remains high. Prenatal diagnosis, essential for risk assessment and organisation of perinatal/postnatal care, offers parents the opportunity to consider the termination of pregnancy. In times of quick changes in prenatal screening programmes, it is relevant to evaluate the effect of prenatal screening on perinatal mortality rates.

OBJECTIVES

The objective of this study was to study trends in early foetal and perinatal mortality associated with congenital anomalies before/after the introduction of the Dutch prenatal screening programme.

METHODS

This population-based cohort study included 8535 foetuses/neonates with congenital anomalies born in the Northern Netherlands between 2001 and 2017. Total deaths were defined as sum of early foetal (before 24 weeks' gestation) and perinatal deaths (from 24 weeks' gestation till day 7 post-partum). Foetal deaths were categorised into spontaneous or elective termination of pregnancy for foetal anomalies (TOPFA). Trends in total mortality as well as early foetal and perinatal mortality were studied. Joinpoint regression was used to calculate the average annual percentage chance (AAPC) and identify linear trends in mortality within subperiods.

RESULTS

Total and perinatal mortality were 17% and 4%. Total mortality was higher in abnormal karyotype and central nervous system anomalies. We observed an increase in total mortality over time: 11.9% in 2001 versus 21.9% in 2017 (AAPC 2.6, 95% confidence interval [CI] 1.5, 3.7), caused by an increase in early foetal mortality from 5.5% to 19.2% (AAPC 8.7, 95% CI 4.7, 12.9) and a decrease in perinatal mortality from 6.4% to 2.7% (AAPC -5.6, 95% CI -10.0, -1.0). The increase in early foetal mortality reflects an increase in TOPFA from 3.6% to 16.9% (AAPC 8.3, 95% CI 4.2, 12.7), mostly occurring at 13-14 and 20-23 weeks' gestation.

CONCLUSIONS

The introduction of the prenatal screening programme led to a decrease in perinatal mortality among foetuses and neonates with congenital anomalies and a marked increase in early foetal mortality before 24 weeks' gestation due to higher rates of TOPFA.

Interpregnancy interval and prevalence of selected birth defects: A multistate study

BACKGROUND

Both short and long interpregnancy intervals (IPIs) have been associated with adverse birth outcomes. We undertook a multistate study to describe the prevalence of selected birth defects by IPI.

METHODS

We obtained data from nine population-based state birth defects registries for singleton live births in 2000-2009 among mothers with a previous live birth identified through birth certificates. IPI was calculated as the difference between prior birthdate and start of the current pregnancy (conception date). We estimated prevalence of selected defects per 10,000 live births and prevalence ratios (PRs) with 95% confidence intervals (CIs) overall and stratified by maternal age at previous birth and race/ethnicity. Primary analyses focused on short IPI < 6 months and long IPI ≥ 60 months compared to 18-23 months (referent). Sensitivity analyses limited to active-surveillance states and those with<10% missing IPI.

RESULTS

Among 5,147,962 eligible births, 6.3% had short IPI while 19.8% had long IPI. Compared to referent, prevalence with short IPI was elevated for gastroschisis (3.7, CI: 3.0-4.5 vs. 2.0, CI: 1.6-2.4) and with both short and long IPI for tetralogy of Fallot (short: 3.4, 2.8-4.2 long: 3.8, 3.4-4.3 vs. 2.7, 2.3-3.2) and cleft lip ± palate (short: 9.9, 8.8-11.2 long: 9.2, 8.5-9.8 vs. 8.4, 7.6-9.2). Stratified analyses identified additional associations, including elevated prevalence of anencephaly with short IPI in younger mothers and limb defects with long IPI in those ages 25-34 at prior birth. Sensitivity analyses showed similar results.

CONCLUSION

In this population-based study, we observed increased prevalence of several birth defects with short and long IPI.

Maternal and offspring genetic risk score analyses of fetal alcohol exposure and attention-deficit hyperactivity disorder risk in offspring

Background

Studies investigating the effects of prenatal alcohol exposure on childhood attention‐deficit hyperactivity disorder (ADHD) symptoms using conventional observational designs have reported inconsistent findings, which may be affected by unmeasured confounding and maternal and fetal ability to metabolize alcohol. We used genetic variants from the alcohol metabolizing genes, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), as proxies for fetal alcohol exposure to investigate their association with risk of offspring ADHD symptoms around age 7–8 years.

Methods

We used data from 3 longitudinal pregnancy cohorts: Avon Longitudinal Study of Parents and Children (ALSPAC), Generation R study (GenR), and the Norwegian Mother, Father and Child Cohort study (MoBa). Genetic risk scores (GRS) for alcohol use and metabolism using 36 single nucleotide polymorphisms (SNPs) from ADH and ALDH genes were calculated for mothers (N_ALSPAC = 8196; N_MOBA = 13,614), fathers (N_MOBA = 13,935), and offspring (N_ALSPAC=8,237; N_MOBA=14,112; N_GENR=2,661). Associations between maternal GRS and offspring risk of ADHD symptoms were tested in the full sample to avoid collider bias. Offspring GRS analyses were stratified by maternal drinking status.

Results

The pooled estimate in maternal GRS analyses adjusted for offspring GRS in ALSPAC and MoBa was OR = 0.99, 95%CI 0.97–1.02. The pooled estimate in offspring GRS analyses stratified by maternal drinking status across all the cohorts was as follows: OR_DRINKING = 0.98, 95% CI 0.94–1.02; OR_{NO DRINKING} = 0.99, 95% CI 0.97–1.02. These findings remained similar after accounting for maternal genotype data in ALSPAC and maternal and paternal genotype data in MoBa.

Conclusions

We did not find evidence for a causal effect of fetal alcohol exposure on risk of ADHD symptoms in offspring. The results may be affected by limited power to detect small effects and outcome assessment.

The implications of outcome truncation in reproductive medicine RCTs: a simulation platform for trialists and simulation study

BACKGROUND

Randomised controlled trials in reproductive medicine are often subject to outcome truncation, where the study outcomes are only defined in a subset of the randomised cohort. Examples include birthweight (measurable only in the subgroup of participants who give birth) and miscarriage (which can only occur in participants who become pregnant). These outcomes are typically analysed by making a comparison between treatment arms within the subgroup (for example, comparing birthweights in the subgroup who gave birth or miscarriages in the subgroup who became pregnant). However, this approach does not represent a randomised comparison when treatment influences the probability of being observed (i.e. survival). The practical implications of this for the design and interpretation of reproductive trials are unclear however.

METHODS

We developed a simulation platform to investigate the implications of outcome truncation for reproductive medicine trials. We used this to perform a simulation study, in which we considered the bias, type 1 error, coverage, and precision of standard statistical analyses for truncated continuous and binary outcomes. Simulation settings were informed by published assisted reproduction trials.

RESULTS

Increasing treatment effect on the intermediate variable, strength of confounding between the intermediate and outcome variables, and the presence of an interaction between treatment and confounder were found to adversely affect performance. However, within parameter ranges we would consider to be more realistic, the adverse effects were generally not drastic. For binary outcomes, the study highlighted that outcome truncation could cause separation in smaller studies, where none or all of the participants in a study arm experience the outcome event. This was found to have severe consequences for inferences.

CONCLUSION

We have provided a simulation platform that can be used by researchers in the design and interpretation of reproductive medicine trials subject to outcome truncation and have used this to conduct a simulation study. The study highlights several key factors which trialists in the field should consider carefully to protect against erroneous inferences. Standard analyses of truncated binary outcomes in small studies may be highly biassed, and it remains to identify suitable approaches for analysing data in this context.

Maternal risk factors for congenital limb deficiencies: A population-based case-control study

BACKGROUND

Risk factors for congenital limb deficiencies are poorly understood.

OBJECTIVE

To investigate risk factors for congenital limb deficiencies.

METHODS

We conducted a nationwide population-based case-control (1:5) study in Finland, using national registers on congenital anomalies, births, and induced abortions, cross-linked with data on maternal prescription medicine use obtained from the registers on Reimbursed Drug Purchases and Medical Special Reimbursements. Five hundred and four children with limb deficiencies (241 isolated, 181 syndromic, and 82 other associated anomalies) were identified, and 2,520 controls were matched to cases on residence and year of pregnancy. Non-syndromic cases (n = 323) were subdivided into longitudinal (n = 120), transverse (n = 123), intercalary (n = 24), mixed (n = 18), and unknown (n = 38) deficiencies.

RESULTS

Pregestational diabetes was associated with all limb deficiencies (adjusted odds ratio [OR] 12.71, 95% confidence interval [CI] 2.37, 68.25) and with isolated (OR 11.42, 95% CI 2.00, 64.60) deficiencies. Primiparity was associated with increased risk of congenital limb deficiencies among all cases (OR 1.49, 95% CI 1.15, 1.93), isolated cases (OR 1.46, 95% CI 1.09, 1.96), and among cases with longitudinal (OR 1.90, 95% CI 1.24, 2.90) and transverse deficiencies (OR 1.75, 95% CI 1.13, 2.70). Young maternal age (<25 years) was associated with all congenital limb deficiencies (OR 1.40, 95% CI 1.02, 1.90) and transverse deficiencies (OR 1.76, 95% CI 1.05, 2.96). Advanced maternal age (≥35 years) was associated with syndromic (OR 1.82, 95% CI 1.19, 2.78) and transverse deficiencies (OR 1.94, 95% CI 1.06, 3.57). Maternal antiepileptic medication was associated with all (OR 5.77, 95% CI 1.75, 19.04) and with isolated cases (OR 3.83, 95% CI 1.02, 14.34).

CONCLUSIONS

It is important that pregnant women taking medications, especially antiepileptics, or women with pregestational diabetes are carefully monitored with regard to the occurrence and risk of limb deficiencies in the fetus.

Original article: is the protective association between hyperemesis gravidarum and birth defects biased by pregnancy termination?

PURPOSE

We assessed whether the protective association between hyperemesis gravidarum and birth defects could be due to selection bias from exclusion of pregnancy terminations.

METHODS

We designed a cohort study of 2,115,581 live births in Canada, 1990-2016. The main exposure measure was hyperemesis gravidarum. The main outcome measure included any birth defect at delivery. We estimated risk ratios (RR) and 95% confidence intervals (CI) for the association of hyperemesis gravidarum with birth defects in log-binomial regression models, and assessed the extent of selection bias through correction factors.

RESULTS

Hyperemesis gravidarum was associated with 0.88 times the risk of birth defects in models not corrected for bias (95% CI 0.82-0.94). Correction for selection bias suggested that if screening for birth defects was associated with 1.33 times the chance of detecting birth defects and having a pregnancy termination, there would be no association with hyperemesis gravidarum. If ultrasound was associated with 2.00 times the chance of detecting birth defects and 1.50 times the risk of pregnancy termination, hyperemesis gravidarum would be associated with 1.27 times the risk of birth defects (95% CI 1.18-1.35).

CONCLUSIONS

The protective association between hyperemesis gravidarum and birth defects in previous studies may be due to selection bias.

Hydroxychloroquine early in pregnancy and risk of birth defects

BACKGROUND

Hydroxychloroquine is generally considered safe in pregnancy for the treatment of rheumatic conditions, but studies have been too small to evaluate teratogenicity. Quantifying the risk of congenital malformations associated with early pregnancy exposure to hydroxychloroquine is important in both the context of its ongoing use for rheumatological disorders and its potential future use for coronavirus disease 2019 prophylaxis, for which a number of clinical trials are ongoing despite initial trials for coronavirus disease 2019 treatment having been negative.

OBJECTIVE

The study objective was to evaluate the risk of major congenital malformations associated with exposure to hydroxychloroquine during the first trimester of pregnancy, the period of organogenesis.

STUDY DESIGN

We performed a population-based cohort study nested in the Medicaid Analytic eXtract (MAX, 2000-2014) and IBM MarketScan Research Database (MarketScan, 2003-2015). The source cohort included 2045 hydroxychloroquine-exposed pregnancies and 3,198,589 pregnancies not exposed to hydroxychloroquine continuously enrolled in their respective insurance program for 3 months before the last menstrual period through at least 1 month after delivery; infants were enrolled for at least 3 months after birth. We compared the risk of congenital malformations in women using hydroxychloroquine during the first trimester of pregnancy with that of those not using hydroxychloroquine, restricting the cohort to women with rheumatic disorders and using propensity score matching to control for indication, demographics, medical comorbidities, and concomitant medications (1867 hydroxychloroquine-exposed pregnancies and 19,080 pregnancies not exposed to hydroxychloroquine). The outcomes considered included major congenital malformations diagnosed during the first 90 days after delivery and specific malformation types for which there were at least 5 exposed events: oral cleft, cardiac, respiratory, gastrointestinal, genital, urinary, musculoskeletal, and limb defects.

RESULTS

Overall, 54.8 per 1000 infants exposed to hydroxychloroquine were born with a major congenital malformation versus 35.3 per 1000 unexposed infants, corresponding to an unadjusted relative risk of 1.51 (95% confidence interval, 1.27-1.81). Patient characteristics were balanced in the restricted, propensity score-matched cohort. The adjusted relative risk was 1.26 (95% confidence interval, 1.04-1.54); it was 1.33 (95% confidence interval, 1.08-1.65) for a daily dose of ≥400 mg and 0.95 (95% confidence interval, 0.60-1.50) for a daily dose of <400 mg. Among the different malformation groups considered, more substantial increases in the risk of oral clefts, respiratory anomalies, and urinary defects were observed, although estimates were imprecise. No pattern of malformation was identified.

CONCLUSION

Our findings suggest a small increase in the risk of malformations associated with first-trimester hydroxychloroquine use. For most patients with autoimmune rheumatic disorders, the benefits of treatment during pregnancy will likely outweigh this risk. If hydroxychloroquine were shown to be effective for coronavirus disease 2019 prophylaxis in ongoing trials, the risk of malformations would need to be balanced against such benefits.

Association of Improved Periconception Hemoglobin A1c With Pregnancy Outcomes in Women With Diabetes

IMPORTANCE

Prepregnancy diabetes is associated with higher perinatal and maternal morbidity, especially if periconception glycemic control is suboptimal. It is not known whether improved glycemic control from preconception to early pregnancy and midpregnancy periods can reduce the risk of adverse perinatal and maternal outcomes.

OBJECTIVE

To determine whether a net decline in glycated hemoglobin A1c (HbA1c) from preconception to the first half of pregnancy is associated with a lower risk of adverse outcomes for mother and child.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cohort study was completed in all of Ontario, Canada, from 2007 to 2018. Included were births among women with prepregnancy diabetes whose HbA1c was measured within 90 days preconception and again from conception through 21 weeks completed gestation (early pregnancy to midpregnancy). Statistical analysis was performed from July to September 2020.

EXPOSURES

Net decrease in HbA1c from preconception to early pregnancy and midpregnancy.

MAIN OUTCOMES AND MEASURES

The main outcome was a congenital anomaly from birth to age 1 year. Other outcomes included preterm birth or perinatal mortality among offspring as well as severe maternal morbidity (SMM) or death among mothers. Adjusted relative risks (aRRs) were calculated per 0.5% absolute net decline in HbA1c from preconception up to early pregnancy and midpregnancy, adjusting for maternal age at conception, preconception HbA1c and hemoglobin concentration, and gestational age at HbA1c measurement.

RESULTS

A total of 3459 births were included, with a mean (SD) maternal age of 32.6 (5.0) years at conception. Overall, the mean (SD) HbA1c decreased from 7.2% (1.6%) preconception to 6.4% (1.1%) in early pregnancy to midpregnancy. There were 497 pregnancies (14.4%) with a congenital anomaly, with an aRR of 0.94 (95% CI, 0.89-0.98) per 0.5% net decrease in HbA1c, including for cardiac anomalies (237 infants; aRR, 0.89; 95% CI, 0.84-0.95). The risk was also reduced for preterm birth (847 events; aRR, 0.89; 95% CI, 0.86-0.91). SMM or death occurred among 191 women (5.5%), with an aRR of 0.90 (95% CI, 0.84-0.96) per 0.5% net decrease in HbA1c.

CONCLUSIONS AND RELEVANCE

These findings suggest that women with prepregnancy diabetes who achieve a reduction in HbA1c may have improved perinatal and maternal outcomes. Further study is recommended to determine the best combination of factors, such as lifestyle changes and/or glucose-lowering medications, that can influence periconception HbA1c reduction.

Epidemiological Studies on Fetal Loss - Better Data and Research Methods are Needed

In perinatal epidemiology, fetal deaths occur over the first timeline, from conception to birth or fetal death. Majority of other epidemiological research on human diseases focus on the second timeline, from birth to death. The transition from the first to the second timeline is not a fixed duration of time and it depends on when birth occurs. We discussed the complications when switching from the first to the second timeline in epidemiological studies of early life exposures, pregnancy events, and future health outcomes. Population-based studies often lack accurate data on the date of conception for most pregnancies and the complete count of fetal death, leading to chances for selection and misclassification biases. To address these problems, better research data and methodological advancement in study designs and biases evaluations are needed.