Constructing Causal Diagrams for Common Perinatal Outcomes: Benefits, Limitations and Motivating Examples with Maternal Antidepressant Use in Pregnancy

The relationship between crowding in the delivery ward and the risk of postpartum hemorrhage

INTRODUCTION

Postpartum hemorrhage (PPH) is a key concern in maternal health, with early identification important for preventing severe complications. In a crowded delivery ward, where the number of births exceeds the normal range, labor management, and PPH prevention may be compromised. Although previous research has mainly focused on crowding over the entire day, it remains unclear whether crowding in the hours surrounding birth influences PPH risk. Therefore, our study aimed to assess the association between delivery ward crowding, adjacent to birth, and PPH and to explore whether births during periods of potentially lower staffing, such as summer months or weekends, could amplify this risk.

MATERIAL AND METHODS

This case-control study included 1 027 620 births in Sweden (2004-2019) from the Medical Birth Register. PPH, defined as estimated blood loss >1000 mL, cases were identified using a diagnostic code for PPH and were matched (1:10) with controls by the standardization criteria: delivery ward, year, and time of birth (night/day). The secondary outcome was PPH with blood transfusion. After standardization, crowding was defined as the number of births in a ±2-h interval around the index birth exceeding the 75th percentile. Unadjusted conditional logistic regression was used to study the association between crowding and PPH, PPH with blood transfusion, and to examine whether giving birth during a weekend or summer vacation month (June-August) modified these associations. Results were presented as odds ratios (OR) with 95% confidence intervals (CI).

RESULTS

Labor induction and emergency cesarean delivery were less common in births that occurred during crowded compared to noncrowded time intervals. Crowding was not associated with an increased risk of PPH (OR: 0.97; 95% CI: 0.95-0.99) or PPH with blood transfusion (OR: 0.99; 95% CI: 0.92-1.07). Giving birth during a summer month or a weekend did not change the estimates for the association between crowding and PPH.

CONCLUSIONS

Focusing on a narrow time frame around birth, crowding in the delivery ward was not associated with an increased, but instead a modest reduction, in risk of PPH. Future studies should investigate how staffing in relation to crowding influences the risk of PPH and other adverse birth outcomes.

Building a better model: abandon kitchen sink regression

This paper critically examines 'kitchen sink regression', a practice characterised by the manual or automated selection of variables for a multivariable regression model based on p values or model-based information criteria. We highlight the pitfalls of this method, using examples from perinatal/neonatal medicine, and propose more robust alternatives. The concept of directed acyclic graphs (DAGs) is introduced as a tool for describing and analysing causal relationships. We highlight five key issues with 'kitchen sink regression': (1) the disregard for the directionality of variable relationships, (2) the lack of a meaningful causal interpretation of effect estimates from these models, (3) the inflated alpha error rate due to multiple testing, (4) the risk of overfitting and model instability and (5) the disregard for content expertise in model building. We advocate for the use of DAGs to guide variable selection for models that aim to examine associations between a putative risk factor and an outcome and emphasise the need for a more thoughtful and informed use of regression models in medical research.

Racial/ethnic differences in the clinical presentation and survival of breast cancer by subtype

Background

Breast cancer (BC) affects racial and ethnic groups differently, leading to disparities in clinical presentation and outcomes. It is unclear how Hispanic ethnicity affects BC outcomes based on geographic location and proximity to the United States (U.S.)/Mexico border. We hypothesized that the impact of race/ethnicity on BC outcomes depends on geographic location and country of origin within each BC subtype.

Methods

We analyzed BC data from the Texas Cancer Registry by race/ethnicity/birthplace according to BC subtype (luminal A/luminal B/human epidermal growth factor receptor 2 [HER2]/triple-negative breast cancer[TNBC]). Other covariates included age, geographic location (U.S., Mexico), residency (border, non-border), treatments, and comorbidities. Crude and adjusted effects of race/ethnicity and birthplace on overall survival (OS) were analyzed using Cox regression methods.

Results

Our analysis of 76,310 patient records with specific BC subtypes revealed that Hispanic and non-Hispanic Black (NHB) patients were diagnosed at a younger age compared with non-Hispanic White (NHW) patients for all BC subtypes. For the 19,748 BC patients with complete data on race/ethnicity/birthplace/residency, Hispanic patients had a higher mortality risk in the Luminal A subtype, regardless of birthplace, whereas U.S.-born Hispanics had a higher risk of death in the TNBC subtype. In contrast, NHB patients had a higher mortality risk in the Luminal A and HER2 subtypes. Residence along the U.S./Mexico border had little impact on OS, with better outcomes in Luminal A patients and worse outcomes in Luminal B patients aged 60-74 years.

Conclusion

Race/ethnicity, geographic birth location, and residency were significant predictors of survival in BC. Migration, acculturation, and reduced healthcare access may contribute to outcome differences.

Associations of periconceptional oral contraceptive use with pregnancy complications and adverse birth outcomes

BACKGROUND

Periconceptional use of oral contraceptives (OCs) has been reported to increase risks of pregnancy complications and adverse birth outcomes, but risks are suggested to differ depending on the timing of discontinuation, amount of oestrogen and progestin content.

METHODS

Prospective cohort study among 6470 pregnancies included in the PRegnancy and Infant DEvelopment (PRIDE) Study in 2012-19. Exposure was defined as any reported use of OCs within 12 months pre-pregnancy or after conception. Outcomes of interest were gestational diabetes, gestational hypertension, pre-eclampsia, pre-term birth, low birthweight and small for gestational age (SGA). Multivariable Poisson regression using stabilized inverse probability weighting estimated relative risks (RRs) with 95% CIs.

RESULTS

Any periconceptional OC use was associated with increased risks of pre-eclampsia (RR 1.38, 95% CI 0.99-1.93), pre-term birth (RR 1.38, 95% CI 1.09-1.75) and low birthweight (RR 1.45, 95% CI 1.10-1.92), but not with gestational hypertension (RR 1.09, 95% CI 0.91-1.31), gestational diabetes (RR 1.02, 95% CI 0.77-1.36) and SGA (RR 0.96, 95% CI 0.75-1.21). Associations with pre-eclampsia were strongest for discontinuation 0-3 months pre-pregnancy, for OCs containing ≥30 µg oestrogen and for first- or second-generation OCs. Pre-term birth and low birthweight were more likely to occur when OCs were discontinued 0-3 months pre-pregnancy, when using OCs containing <30 µg oestrogen and when using third-generation OCs. Associations with SGA were observed for OCs containing <30 µg oestrogen and for third- or fourth-generation OCs.

CONCLUSIONS

Periconceptional OC use, particularly those containing oestrogen, was associated with increased risks of pre-eclampsia, pre-term birth, low birthweight and SGA.

Mediation Analysis of Maternal Smoking, Gestational Age, and Birth Weight on the Texas-Mexico Border

OBJECTIVES

Published data on the indirect effect of maternal smoking on birth weight as mediated by gestational age in Hispanic populations are lacking. Our goal was to conduct such a mediation analysis using data from El Paso County, Texas.

METHODS

El Paso County is located on the US-Mexico border. A simple mediation analysis was conducted using year 2010 El Paso County birth certificate data. The SAS macro PROCESS 3.5.3 was used to estimate the direct and indirect effects of active maternal smoking (by trimester) on birth weight (in grams) in the setting of linear regression. The single mediator was gestational age in weeks. A direct or indirect effect was deemed to be present if the 95% confidence limits (CLs) excluded 0. Analyses were adjusted for multiple variables, including maternal prepregnancy body mass index. The indirect effect was reported along with a 95% bootstrap CL.

RESULTS

A total of 16,654 singleton births were included in the cohort. The majority of the mothers were White Hispanic (87.2%). The mean (standard deviation) birth weight was 3198.6 g (517.2). A direct effect of maternal smoking during each trimester on birth weight was detected. An indirect effect of maternal smoking on birth weight was not detected in any of the trimesters. In adjusted analyses for the third trimester, the indirect effect for every 1-U increase in the mean number of cigarettes smoked per day was -4.18 (95% bootstrap CL -10.64 to 1.99).

CONCLUSIONS

In our large, predominantly Hispanic cohort, it appears that gestational age is not a mediator of the effect of maternal smoking on birth weight. Future studies in our population should explore other possible mediators of this association.

Association of Caesarean delivery and breastfeeding difficulties during the delivery hospitalization: a community-based cohort of women and full-term infants in Alberta, Canada

OBJECTIVE

Breastfeeding difficulties are the most common reason for breastfeeding cessation, particularly in the early postpartum. Caesarean delivery is associated with earlier breastfeeding cessation than is the case with vaginal delivery, but differences in breastfeeding difficulties by mode of delivery have not been thoroughly examined. Our objective was to explore the association between Caesarean delivery and types of breastfeeding difficulties.

METHODS

We conducted a secondary analysis of data from a prospective cohort study of mothers who delivered full-term, singleton infants in Calgary, Alberta, Canada (N = 418). Women completed self-report questionnaires during the delivery hospitalization. Mode of delivery was defined as vaginal or Caesarean, and further classified as planned or unplanned Caesarean. Breastfeeding difficulties were measured using the Breastfeeding Experiences Scale and operationalized with binary variables for presence of various types of maternal (i.e. physical, supply, social) and infant (i.e. latch, behaviour/health) difficulties that were reported as moderate to unbearable. Multivariable logistic regression was used to estimate adjusted odds ratios (AORs) and 95% confidence intervals (CIs).

RESULTS

Overall, 37.1% of women had a Caesarean delivery and 80.9% experienced a breastfeeding difficulty during the delivery hospitalization. Of the difficulties studied, Caesarean delivery was significantly associated with low milk supply (AOR = 1.62, 95% CI = 1.16-2.28) and infant behaviour/health difficulties (AOR = 1.33, 95% CI = 1.01-1.75). The association with low milk supply persisted when examining both planned (AOR = 2.42, 95% CI = 1.19-4.92) and unplanned (AOR = 2.21, 95% CI = 1.16-4.22) Caesarean deliveries.

CONCLUSION

Mothers who deliver by Caesarean have higher odds of reporting low milk supply and infant behaviour/health difficulties than women who deliver vaginally.

Associations Between Late-Onset Preeclampsia and the Use of Calcium-Based Antacids and Proton Pump Inhibitors During Pregnancy: A Prospective Cohort Study

Purpose

Preeclampsia is a leading cause of maternal morbidity and mortality. Calcium-based antacids and proton pump inhibitors (PPIs) are commonly used during pregnancy to treat symptoms of gastroesophageal reflux disease. Both have been hypothesized to reduce the risk of preeclampsia. We determined associations of calcium-based antacid and PPI use during pregnancy with late-onset preeclampsia (≥34 weeks of gestation), taking into account dosage and timing of use.

Patients and Methods

We included 9058 pregnant women participating in the PRIDE Study (2012–2019) or The Dutch Pregnancy Drug Register (2014–2019), two prospective cohorts in The Netherlands. Data were collected through web-based questionnaires and obstetric records. We estimated risk ratios (RRs) for late-onset preeclampsia for any use and trajectories of calcium-based antacid and PPI use before gestational day 238, and hazard ratios (HRs) for time-varying exposures after gestational day 237.

Results

Late-onset preeclampsia was diagnosed in 2.6% of pregnancies. Any use of calcium-based antacids (RR 1.2 [95% CI 0.9–1.6]) or PPIs (RR 1.4 [95% CI 0.8–2.4]) before gestational day 238 was not associated with late-onset preeclampsia. Use of low-dose calcium-based antacids in gestational weeks 0–16 (<1 g/day; RR 1.8 [95% CI 1.1–2.9]) and any use of PPIs in gestational weeks 17–33 (RR 1.6 [95% CI 1.0–2.8]) seemed to increase risks of late-onset preeclampsia. We did not observe associations between late-onset preeclampsia and use of calcium-based antacids (HR 1.0 [95% CI 0.6–1.5]) and PPIs (HR 1.4 [95% CI 0.7–2.9]) after gestational day 237.

Conclusion

In this prospective cohort study, use of calcium-based antacids and PPIs during pregnancy was not found to reduce the risk of late-onset preeclampsia.

Ability of municipality-level deprivation indices to capture social inequalities in perinatal health in France: A nationwide study using preterm birth and small for gestational age to illustrate their relevance

BACKGROUND

Evidence-based policy-making to reduce perinatal health inequalities requires an accurate measure of social disparities. We aimed to evaluate the relevance of two municipality-level deprivation indices (DIs), the French-Deprivation-Index (FDep) and the French-European-Deprivation-Index (FEDI) in perinatal health through two key perinatal outcomes: preterm birth (PTB) and small-for-gestational-age (SGA).

METHODS

We used two data sources: The French National Perinatal Surveys (NPS) and the French national health data system (SNDS). Using the former, we compared the gradients of the associations between individual socioeconomic characteristics (educational level and income) and "PTB and SGA" and associations between municipality-level DIs (Q1:least deprived; Q5:most deprived) and "PTB and SGA". Using the SNDS, we then studied the association between each component of the two DIs (census data, 2015) and "PTB and SGA". Adjusted odds ratios (aOR) were estimated using multilevel logistic regression with random intercept at the municipality level.

RESULTS

In the NPS (N = 26,238), PTB and SGA were associated with two individual socioeconomic characteristics: maternal educational level (≤ lower secondary school vs. ≥ Bachelor's degree or equivalent, PTB: aOR = 1.43 [1.22-1.68], SGA: (1.31 [1.61-1.49]) and household income (< 1000 € vs. ≥ 3000 €, PTB: 1.55 [1.25-1.92], SGA: 1.69 [1.45-1.98]). For both FDep and FEDI, PTB and SGA were more frequent in deprived municipalities (Q5: 7.8% vs. Q1: 6.3% and 9.0% vs. 5.9% for PTB, respectively, and 12.0% vs. 10.3% and 11.9% vs. 10.2% for SGA, respectively). However, after adjustment, neither FDep nor FEDI showed a significant gradient with PTB or SGA. In the SNDS (N = 726,497), no FDep component, and only three FEDI components were significantly associated (specifically, the % of the population with ≤ lower secondary level of education with both outcomes (PTB: 1.5 [1.15-1.96]); SGA: 1.25 [1.03-1.51]), the % of overcrowded (i.e., > 1 person per room) houses (1.63 [1.15-2.32]) with PTB only, and unskilled farm workers with SGA only (1.52 [1.29-1.79]).

CONCLUSION

Some components of FDep and FEDI were less relevant than others for capturing ecological inequalities in PTB and SGA. Results varied for each DI and perinatal outcome studied. These findings highlight the importance of testing DI relevance prior to examining perinatal health inequalities, and suggest the need to develop DIs that are suitable for pregnant women. .

Racial disparities in caesarean delivery among nulliparous women that delivered at term: cross-sectional decomposition analysis of Nebraska birth records from 2005-2014

BACKGROUND

Previous studies suggest higher rates of caesarean section among women who identify as racial/ethnic minorities. The objective of this study was to understand factors contributing to differences in caesarean rates across racial and ethnic groups.

METHODS

Data was collected from 2005 to 2014 Nebraska birth records on nulliparous, singleton births occurring on or after 37 weeks gestation (n = 87,908). Risk ratios (RR) and 95% confidence intervals (CI) for caesarean were calculated for different racial and ethnic categories, adjusting for maternal age, marital status, county of residence, education, insurance status, pre-pregnancy BMI, and smoking status. Fairlie decomposition technique was utilized to quantify the contribution of individual variables to the observed differences in caesarean.

RESULTS

In the adjusted analysis, relative to non-Hispanic (NH) White race, both Asian-NH (RR 1.21, 95% CI 1.14, 1.28) and Black-NH races (RR 1.13, 95% CI 1.08, 1.19) were associated with a significantly higher risk for caesarean. The decomposition analysis showed that among the variables assessed, maternal age, education, and pre-pregnancy BMI contributed the most to the observed differences in caesarean rates across racial/ethnic groups.

CONCLUSION

This analysis quantified the effect of social and demographic factors on racial differences in caesarean delivery, which may guide public health interventions aimed towards reducing racial disparities in caesarean rates. Interventions targeted towards modifying maternal characteristics, such as reducing pre-pregnancy BMI or increasing maternal education, may narrow the gap in caesarean rates across racial and ethnic groups. Future studies should determine the contribution of physician characteristics, hospital characteristics, and structural determinants of health towards racial disparities in caesarean rates.

Association of Timing and Duration of Prenatal Analgesic Opioid Exposure With Attention-Deficit/Hyperactivity Disorder in Children

IMPORTANCE

Prior studies have reported that the use of illicit opioids during pregnancy is associated with increased risk of attention-deficit/hyperactivity disorder (ADHD) in offspring; however, evidence regarding the association of analgesic opioids is limited.

OBJECTIVE

To examine the association of timing and duration of prenatal analgesic opioid exposure with ADHD in children.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study uses data from the Norwegian Mother, Father and Child Cohort study (1999-2008), a nationwide birth cohort study linked to national health registries, with a mean (SD) follow-up of 10.8 (2.2) years. A total of 73 784 live-born singleton children born to 62 013 mothers who reported a pain-related condition before and/or during pregnancy were included, with 2 comparator groups: (1) mothers who did not use any opioids and (2) mothers who used opioids before pregnancy only. Data were analyzed from June to December 2020.

EXPOSURES

Maternal self-report of analgesic opioid use during pregnancy, by timing (early and middle and/or late) and duration (≥5 weeks vs ≤4 weeks).

MAIN OUTCOMES AND MEASURES

Diagnosis of ADHD or filled prescription for ADHD medication in children and symptoms of ADHD at child age 5 years, measured by Conners' Parent Rating Scale-Revised. Inverse probability of treatment weights were used to control for measured confounding. Cox regression was used to estimate hazard ratios (HRs) and 95% CIs.

RESULTS

The analyses of ADHD diagnosis and ADHD symptoms included 73 480 children (35 996 [49.0%] girls; mean [SD] maternal age, 30.0 [4.6] years) and 31 270 children (15 377 [49.2%] girls; mean [SD] maternal age, 30.5 [4.4] years), respectively. Overall, 1726 children in the ADHD diagnosis sample (2.3%) and 667 children in the ADHD symptom sample (2.1%) were exposed to an analgesic opioid at least once during gestation. No associations between timing of prenatal analgesic opioid exposure and ADHD diagnosis or symptoms was found. Exposure for 5 or more weeks was associated with an increased risk of ADHD diagnosis (HR, 1.60, 95% CI, 1.04-2.47) compared with exposure for 4 weeks or less; however, there was no such association for the risk of ADHD symptoms.

CONCLUSIONS AND RELEVANCE

In this cohort study, a slightly elevated risk of ADHD diagnosis after prenatal analgesic opioid exposure for 5 or more weeks was found compared with exposure for 4 weeks or less. This result may be driven by longer duration of use; however, the role of residual or unmeasured confounding cannot be excluded. This finding needs to be replicated in other studies.

Quantifying the influence of bias in reproductive and perinatal epidemiology through simulation

PURPOSE

The application of simulated data in epidemiological studies enables the illustration and quantification of the magnitude of various types of bias commonly found in observational studies. This was a review of the application of simulation methods to the quantification of bias in reproductive and perinatal epidemiology and an assessment of value gained.

METHODS

A search of published studies available in English was conducted in August 2020 using PubMed, Medline, Embase, CINAHL, and Scopus. A gray literature search of Google and Google Scholar, and a hand search using the reference lists of included studies was undertaken.

RESULTS

Thirty-nine papers were included in this study, covering information (n = 14), selection (n = 14), confounding (n = 9), protection (n = 1), and attenuation bias (n = 1). The methods of simulating data and reporting of results varied, with more recent studies including causal diagrams. Few studies included code for replication.

CONCLUSIONS

Although there has been an increasing application of simulation in reproductive and perinatal epidemiology since 2015, overall this remains an underexplored area. Further efforts are required to increase knowledge of how the application of simulation can quantify the influence of bias, including improved design, analysis and reporting. This will improve causal interpretation in reproductive and perinatal studies.

Are small-for-gestational-age preterm infants at increased risk of overweight? Statistical pitfalls in overadjusting for body size measures

OBJECTIVE

The objective of this study is to analyze the effect of adjusting for body measures on the association between small for gestational age (SGA) and overweight at 3 years.

STUDY DESIGN

Data were obtained from the Preterm Infant Multicenter Growth Study (n = 1089). Logistic regression was used, to adjust for confounders with additional adjustments separately for weight and height at 21 months. Marginal structural models (MSMs) estimated the direct effect of SGA on overweight.

RESULTS

The crude and adjusted for confounders models yielded null associations between SGA and overweight. Adjusting for height yielded a positive association (odds ratio (OR): 2.31, 95% CI: 0.52-10.26) and adjusting for weight provided a significantly positive association (OR: 6.60, 95% CI: 1.10-37.14). The MSMs, with height and weight held constant, provided no evidence for a direct effect of SGA on overweight (OR: 0.83, 95% CI: 0.14-5.01, OR: 0.71, 95% CI: 0.18-2.81, respectively).

CONCLUSION

Adjusting for body measures can change the association between SGA and overweight, providing spurious estimates.

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.

The reporting of observational studies of drug effectiveness and safety: recommendations to extend existing guidelines

INTRODUCTION

The use of observational data to assess drug effectiveness and safety can provide relevant information, much of which may not be feasible to obtain through randomized clinical trials. Because observational studies provide critical drug safety and effectiveness information that influences drug policy and prescribing practices, transparent, consistent, and accurate reporting of these studies is critical.

AREAS COVERED

We provide recommendations to extend existing reporting guidelines, covering the main components of primary research studies (methods, results, discussion).

EXPERT OPINION

Our recommendations include extending drug safety and effectiveness guidelines to include explicit checklist items on: study registration, causal diagrams, rationale for measures of effect, comprehensive assessment of bias, comprehensive data cleaning steps, drug equivalents, subject-level drug data visualization, sex and gender-based analyses and results, patient-oriented outcomes, and patient involvement in research.

Maternal persistent marijuana use and cigarette smoking are independently associated with shorter gestational age

BACKGROUND

Research assessing the effects of marijuana use on preterm birth has found mixed results, in part, due to lack of attention to the role of maternal tobacco smoking during pregnancy.

OBJECTIVES

The study objective was to investigate whether maternal marijuana use was independently associated with gestational age, preterm birth, and two preterm birth subtypes (spontaneous vs clinician-initiated).

METHODS

Participants included 8261 mother-newborn pairs from the Boston Birth Cohort. Information on gestational age was collected from electronic medical records. Marijuana use and tobacco smoking during pregnancy were assessed through a standard questionnaire after birth. Linear and log-linear regression models were used to assess associations between marijuana use with and without tobacco smoking during pregnancy and the outcomes of interest.

RESULTS

Of the 8261 mothers, 27.5% had preterm births. About 3.5% of mothers with term deliveries and 5.2% of mothers with preterm births used marijuana during pregnancy. Marijuana use and cigarette smoking were independently associated with a decrease in gestational age by 0.50 weeks (95% confidence interval [CI] -0.87, -0.13) and 0.52 weeks (95% CI -0.76, -0.28), respectively. Marijuana use during early or late pregnancy was associated with a similar decrease in gestational age by 0.50 weeks. When we examined the effects on the preterm birth subtypes, simultaneous marijuana use and tobacco smoking were associated with higher risk of spontaneous preterm birth (RR 1.64, 95% CI 1.23, 2.18). The elevated risk was not observed with clinician-initiated preterm birth.

CONCLUSIONS

In this high-risk US population, maternal marijuana use and cigarette smoking during pregnancy were independently associated with shorter gestational age. When we examined the effects on preterm birth subtypes, the elevated risk was only observed with spontaneous preterm birth.

Examining the trimester-specific effects of low gestational weight gain on birthweight: the BOSHI study

Low gestational weight gain (GWG) is a known risk factor of low birthweight. Although studies have previously examined the associations between GWG and birthweight, the period-specific effects of low GWG in each trimester remain unclear. This study aimed to quantify the trimester-specific direct effects of low GWG in Japanese women on birthweight. Using perinatal data from a cohort study, we analyzed pregnant women delivered at an obstetrics/gynecology hospital between October 2006 and May 2010. We focused on women with a pre-pregnancy body mass index (BMI) below 25 kg/m2. The exposure was low GWG. The gestation period was subdivided into trimesters, and the direct effects of low trimester-specific GWG on birthweight were estimated using marginal structural models. These models were guided by a direct acyclic graph that incorporated potential confounders, including pre-pregnancy BMI, age, smoking during pregnancy, height, and parity. We analyzed 563 women and their families. The mean cumulative GWG by the end of the first, second, and third trimesters was 0.9, 6.2, and 10.7 kg, respectively. Approximately 14.0% of the women gained total weight below the range recommended by Japanese Ministry of Health, Labour and Welfare. The direct effects of low GWG on birthweight were 65.9 g (95% confidence interval: 11.4, 120.5), -195.4 g (-263.4, -127.4), and -188.8 g (-292.0, -85.5) for the first, second, and third trimesters, respectively. Insufficient weight gain in the second and third trimesters had a negative impact on birthweight after adjusting for pre-pregnancy BMI and other covariates.

Interpreting the pharmacoepidemiology literature in obstetrical studies: A guide for clinicians

Many prescribers are knowledgeable about randomized controlled trials (RCT), but are less familiar with pharmacoepidemiology studies; that is, observational studies in which a pharmacologic agent is the exposure of interest. To date, few clinical trials include pregnant women. With the absence of RCT data, prescribers must largely rely on the pharmacoepidemiology literature to guide prescribing decisions for pregnant patients. We describe different types of pharmacoepidemiology studies and present a flowchart and table checklist to support clinicians to assess the quality of, and thus the validity of conclusions from, pharmacoepidemiology studies. We provide illustrative examples of published observational studies examining antidepressant treatment during pregnancy and fetal and infant outcomes.

Advances in Epidemiological Methods and Utilisation of Large Databases: A Methodological Review of Observational Studies on Central Nervous System Drug Use in Pregnancy and Central Nervous System Outcomes in Children

INTRODUCTION

Studies have used various epidemiological approaches to study associations between central nervous system (CNS) drug use in pregnancy and CNS outcomes in children. Studies have generally focused on clinical adverse effects, whereas variations in methodologies have not received sufficient attention.

OBJECTIVE

Our objective was to review the methodological characteristics of existing studies to identify any limitations and recommend further research.

METHODS

A systematic literature search was conducted on observational studies listed in PubMed from 1 January 1946 to 21 September 2017. Following independent screening and data extraction, we conducted a review addressing the trends of relevant studies, differences between various data sources, and methods used to address bias and confounders; we also conducted statistical analyses.

RESULTS

In total, 111 observational studies, 25 case-control studies, and 86 cohort studies were included in the review. Publications dating from 1978 to 2006 mainly focused on antiepileptic drugs, but research on antidepressants increased from 2007 onwards. Only one study focused on antipsychotic use during pregnancy. A total of 46 studies obtained data from an administrative database/registry, 20 from ad hoc disease registries, and 41 from ad hoc clinical samples. Most studies (58%) adjusted the confounding factors using general adjustment, whereas only a few studies used advanced methods such as sibling-matched models and propensity score methods; 42 articles used univariate analyses and 69 conducted multivariable regression analyses.

CONCLUSION

Multiple factors, including different study designs and data sources, have led to inconsistent findings in associations between CNS drug use in pregnancy and CNS outcomes in children. Researchers should allow for study designs with clearly defined exposure periods, at the very least in trimesters, and use advanced confounding adjustment methodology to increase the accuracy of the findings.

Neonatal Risk in Children of Women With Congenital Heart Disease: A Cohort Study With Focus on Socioeconomic Status

Background

We hypothesized that women with congenital heart disease (CHD) are at increased risk of giving birth preterm, including very and moderately preterm and giving birth to infants small for gestational age (SGA). We aimed to investigate this in a nation‐wide study with focus on the potential modifying effect of socioeconomic status.

Methods and Results

We performed a cohort study using Danish nation‐wide registers between 1997 and 2014. The exposure, maternal CHD, was subdivided into simple, moderate and complex based on severity of defects. Outcomes were preterm birth and SGA. Cox regression was used to estimate hazard ratios (HR). A total of 933 149 births including 3745 births among women with CHD were studied. The risk of giving birth preterm and SGA were higher among women with CHD as compared with women without CHD; for example, adjusted hazard ratios of preterm birth according to severity: simple 1.33 (95% CI, 1.11–1.59), moderate 1.45 (95% CI, 1.14–1.83) and complex 3.26 (95% CI, 2.41–4.40). Same pattern was seen for very and moderately preterm births and SGA. Education was a strong predictor of both preterm birth and SGA but did not modify the association between maternal congenital heart disease and preterm birth (P=0.38) or SGA (P=0.99).

Conclusions

Women with CHD were at increased risk of preterm birth both, moderately and very preterm, as well as giving birth to infants SGA. Education was a strong predictor of both preterm birth and SGA but the association between CHD and risk of preterm birth and SGA was independent of educational level.

Maternal HBsAg carriers and adverse pregnancy outcomes: A hospital-based prospective cohort analysis

It is not clear whether chronic hepatitis B virus (HBV) infection during pregnancy can increase the risk of adverse pregnancy outcomes for both mothers and neonates. We conducted a hospital-based prospective cohort study on pregnant women (PW) and used an analysis strategy that was guided by directed acyclic graphs (DAGs). Maternal characteristics and major adverse pregnancy outcomes were collected both from questionnaires and hospital-based electronic medical records. Serum hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) status were determined. In total, 3329 of the 3416 pregnant women who received routine antenatal care in a hospital setting at baseline, including 346 HBsAg carriers, were available for analysis. Maternal HBsAg carrier status was associated with an increased risk of intrahepatic cholestasis pregnancy [aOR (adjusting odds ratio) = 1.70; 95% CI (confidence interval) = 1.16-2.49], premature rupture of the membranes (aOR = 1.38; 95% CI = 1.00-1.89) and large for gestational age birth aOR = 1.67; 95% CI = 1.17-2.39). The risk of intrahepatic cholestasis remained in pregnant women with either HBeAg-positive (aOR = 2.96; 95% CI = 1.33-6.62) or HBeAg-negative (aOR = 1.52; 95% CI =1.00-2.32)] status; notably, only maternal HBeAg-negative status was associated with a higher risk of large for gestational age birth (aOR = 1.91; 95% CI = 1.33-2.76). Our results implied that chronic HBV infection during pregnancy may increase the risk of intrahepatic cholestasis of pregnancy, premature rupture of membranes and large for gestational age pregnancies.

Past-month cannabis use among U.S. individuals from 2002-2015: An age-period-cohort analysis

BACKGROUND

Cannabis is the most commonly used illicit drug among U.S. adolescents and adults, but little is known about factors that drive trends in cannabis use prevalence. To better understand drivers of these trends, we aimed to estimate age, period, and cohort effects on past-month cannabis use among U.S. individuals age 12 and older from 2002 to 2015.

METHODS

We conducted an age-period-cohort analysis on past-month cannabis use among participants ages 12 and older using the National Survey on Drug Use and Health (NSDUH), an annual cross-sectional nationally-representative survey of drug use. Additionally, we examined how age, period, and cohort effects differed across gender. Participants (n = 779,799) self-reported cannabis patterns using a computer-assisted telephone interview (CATI).

RESULTS

Past-month cannabis use in this population increased from 6.0% in 2002 to 8.1% in 2015. Distinct age, period, and cohort effects were observed. Compared to participants ages 12-13, participants ages 18-21 (PR: 16.8, 95% CI: 15.6, 18.1) and 22-25 (PR: 13.2, 95% CI: 12.2, 14.4) had dramatically higher prevalence of past-month cannabis use. Compared to participants in 2002, participants in 2014 (PR: 1.2, 95% CI: 1.1, 1.4) and 2014 (PR: 1.2, 95% CI: 1.1, 1.4) had slightly higher prevalence of past-month cannabis use. Compared to the 1940s birth cohort, the 1950s birth cohort (PR: 1.8, 95% CI: 1.5, 2.2) had a higher prevalence of past-month cannabis use.

CONCLUSIONS

Past-month cannabis use is prevalent and increasing among U.S. adults. Distinct age, period, and cohort effects are at play, though age effects are strongest.

Revisiting the Table 2 fallacy: A motivating example examining preeclampsia and preterm birth

BACKGROUND

A "Table Fallacy," as coined by Westreich and Greenland, reports multiple adjusted effect estimates from a single model. This practice, which remains common in published literature, can be problematic when different types of effect estimates are presented together in a single table. The purpose of this paper is to quantitatively illustrate this potential for misinterpretation with an example estimating the effects of preeclampsia on preterm birth.

METHODS

We analysed a retrospective population-based cohort of 2 963 888 singleton births in California between 2007 and 2012. We performed a modified Poisson regression to calculate the total effect of preeclampsia on the risk of PTB, adjusting for previous preterm birth. pregnancy alcohol abuse, maternal education, and maternal socio-demographic factors (Model 1). In subsequent models, we report the total effects of previous preterm birth, alcohol abuse, and education on the risk of PTB, comparing and contrasting the controlled direct effects, total effects, and confounded effect estimates, resulting from Model 1.

RESULTS

The effect estimate for previous preterm birth (a controlled direct effect in Model 1) increased 10% when estimated as a total effect. The risk ratio for alcohol abuse, biased due to an uncontrolled confounder in Model 1, was reduced by 23% when adjusted for drug abuse. The risk ratio for maternal education, solely a predictor of the outcome, was essentially unchanged.

CONCLUSIONS

Reporting multiple effect estimates from a single model may lead to misinterpretation and lack of reproducibility. This example highlights the need for careful consideration of the types of effects estimated in statistical models.

Prenatal triptan exposure and neurodevelopmental outcomes in 5-year-old children: Follow-up from the Norwegian Mother and Child Cohort Study

BACKGROUND

Triptans are commonly used to treat migraine headaches, but data on the long-term safety of these medications during pregnancy are sparse. Triptans have a biologically plausible mechanism for effects on the fetal brain through binding to 5-HT₁ -receptors, and previous studies show increased risks of externalising behaviour problems in toddlers exposed to triptans during pregnancy.

METHODS

We included 3784 children in the Norwegian Mother and Child Cohort Study, whose mothers returned the 5-year-questionnaire and reported a history of migraine or triptan use; 353 (9.3%) mothers reported use of triptans during pregnancy, 1509 (39.9%) reported migraine during pregnancy but no triptan use, and 1922 (50.8%) had migraine prior to pregnancy only. We used linear and log-binomial models with inverse probability weights to examine the association between prenatal triptan exposure and internalising and externalising behaviour, communication, and temperament in 5-year-old children.

RESULTS

Triptan-exposed children scored higher on the sociability trait than unexposed children of mothers with migraine (β 1.66, 95% confidence interval [0.30, 3.02]). We found no other differences in temperament, or increased risk of behaviour or communication problems.

CONCLUSIONS

Contrary to results from previous studies in younger children, we found no increased risk of externalising behaviour problems in 5-year-old children exposed to triptans in fetal life. Triptan-exposed children did have slightly more sociable temperaments, but the clinical meaning of this finding is uncertain.

The Role of Preterm Birth in the Association Between Opioid Maintenance Therapy and Neonatal Abstinence Syndrome

BACKGROUND

Pregnant women treated with methadone as opioid maintenance therapy are more likely than women treated with buprenorphine to deliver preterm. Preterm birth is associated with less risk of neonatal abstinence syndrome (NAS). We sought to assess the role of preterm birth as a mediator of the relationship between in utero exposure to methadone and NAS compared with buprenorphine.

METHODS

We studied 716 women receiving methadone or buprenorphine and delivering liveborn infants at Magee-Womens Hospital, Pittsburgh, Pennsylvania (2013-15). We implemented inverse probability weighted marginal structural models to isolate the role of preterm birth (<37 weeks' gestation). Weights accounted for confounding by maternal age, race, insurance, parity, delivery year, marital, employment, hepatitis C, and smoking status.

RESULTS

Approximately 57% of the cohort were treated with methadone. Preterm birth was more common in methadone-exposed pregnancies (25% versus 14%). The incidence of NAS treatment was higher in methadone compared with buprenorphine-exposed infants (65% vs 49%), and term compared with preterm births (64% vs 36%). For every 100 infants liveborn to mothers treated for opioid dependence, there were 13 excess cases of NAS among infants exposed to methadone compared with buprenorphine (adjusted risk difference [RD] 13.3, 95% confidence interval [CI] 5.7, 20.9). Among term births, this increased to 17 excess cases of NAS in methadone- compared with buprenorphine-exposed (RD 16.7, 95% CI 9.3, 24.0).

CONCLUSION

The further increased risk of NAS associated with methadone use vs buprenorphine in term deliveries emphasises the utility of buprenorphine in clinical settings aimed at decreasing NAS.

A systematic review of maternal antidepressant use in pregnancy and short- and long-term offspring's outcomes

The relative safety of antidepressants during pregnancy has received substantial attention, but most syntheses fail to account for mental illness effects. We aimed to evaluate the literature comparing low birth weight (LBW) and neurodevelopmental and neurobehavioural outcomes for children whose mothers took antidepressants in pregnancy compared to those whose mothers had common mental disorders, or symptoms, but who did not take antidepressants during pregnancy. A systematic review was conducted searching PubMed, MEDLINE, PsycINFO and Embase in January 2015. A modified version of the Newcastle Ottawa Scale was used to assess study quality. Eleven cohort studies were included: four reporting a LBW outcome (all with higher risk of bias) and seven reporting a neurodevelopmental outcome (five with higher risk of bias). We found only limited evidence of gestational age-adjusted LBW in exposed children in two studies which had a higher risk of bias and did not control for depressive symptom severity. Only five (7.5%) neurodevelopmental outcomes and one (12.5%) neurobehavioural outcome showed evidence of a statistically significant effect, three out of four were from studies with a higher risk of bias. There is little robust evidence indicating a detrimental effect of antidepressant use during pregnancy on LBW and neurodevelopmental and neurobehavioural outcomes. More rigorous study designs are needed.

Making fair comparisons in pregnancy medication safety studies: An overview of advanced methods for confounding control

Understanding the safety of medication use during pregnancy relies on observational studies: However, confounding in observational studies poses a threat to the validity of estimates obtained from observational data. Newer methods, such as marginal structural models and propensity calibration, have emerged to deal with complex confounding problems, but these methods have seen limited uptake in the pregnancy medication literature. In this article, we provide an overview of newer advanced methods for confounding control and show how these methods are relevant for pregnancy medication safety studies.

Confounding, causality, and confusion: the role of intermediate variables in interpreting observational studies in obstetrics

Prospective and retrospective cohorts and case-control studies are some of the most important study designs in epidemiology because, under certain assumptions, they can mimic a randomized trial when done well. These assumptions include, but are not limited to, properly accounting for 2 important sources of bias: confounding and selection bias. While not adjusting the causal association for an intermediate variable will yield an unbiased estimate of the exposure-outcome's total causal effect, it is often that obstetricians will want to adjust for an intermediate variable to assess if the intermediate is the underlying driver of the association. Such a practice must be weighed in light of the underlying research question and whether such an adjustment is necessary should be carefully considered. Gestational age is, by far, the most commonly encountered variable in obstetrics that is often mislabeled as a confounder when, in fact, it may be an intermediate. If, indeed, gestational age is an intermediate but if mistakenly labeled as a confounding variable and consequently adjusted in an analysis, the conclusions can be unexpected. The implications of this overadjustment of an intermediate as though it were a confounder can render an otherwise persuasive study downright meaningless. This commentary provides an exposition of confounding bias, collider stratification, and selection biases, with applications in obstetrics and perinatal epidemiology.

Histologic Chorioamnionitis and Bronchopulmonary Dysplasia in Preterm Infants: The Epidemiologic Study on Low Gestational Ages 2 Cohort

OBJECTIVE

To investigate the association between histologic chorioamnionitis (HCA) and bronchopulmonary dysplasia (BPD) in very preterm infants, both in a general population and for those born after spontaneous preterm labor and after preterm premature rupture of membranes (pPROM).

STUDY DESIGN

This study included 2513 live born singletons delivered at 24-31 weeks of gestation from a national prospective population-based cohort of preterm births; 1731 placenta reports were available. HCA was defined as neutrophil infiltrates in the amnion, chorion of the membranes, or chorionic plate, associated or not with funisitis. The main outcome measure was moderate or severe BPD. Analyses involved logistic regressions and multiple imputation for missing data.

RESULTS

The incidence of HCA was 28.4% overall: 38% in cases of preterm labor, 64% in cases of pPROM, and less than 5% in cases of vascular disorders. Overall, the risk of BPD after adjustment for gestational age, sex, and antenatal steroids was reduced for infants with HCA (HCA alone: aOR 0.6 [95% CI 0.4-0.9]; associated with funisitis: aOR 0.5 [95% CI 0.3-0.8]). This finding was explained by the high rate of BPD and low rate of chorioamnionitis among children with fetal growth restriction. HCA was not associated with BPD in the preterm labor (13.4% vs 8.5%; aOR 0.9; 95% CI 0.5-1.8) or in the pPROM group (12.9% vs 12.1%; aOR 0.6; 95% CI 0.3-1.3).

CONCLUSION

In homogeneous groups of infants born after preterm labor or pPROM, HCA is not associated with BPD.