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Abstract
Purpose
To explore a potential interaction between the effect of specific maternal smoking patterns and the presence of antenatal depression, as independent exposures, in causing postpartum depression (PPD).
Methods
This case–control study of participants with singleton term births (N = 51220) was based on data from the 2017–2018 Pregnancy Risk Assessment Monitoring System. Multivariable log-binomial regression models examined the main effects of smoking patterns and self-reported symptoms of antenatal depression on the risk of PPD on the adjusted risk ratio (aRR) scale and tested a two-way interaction adjusting for covariates selected in a directed acyclic graph (DAG). The interaction effects were measured on the additive scale using relative excess risk due to interaction (RERI), the attributable proportion of interaction (AP), and the synergy index (SI). Causal effects were defined in a counterfactual framework. The E-value quantified the potential impact of unobserved/unknown covariates, conditional on observed covariates.
Results
Among 6841 women in the sample who self-reported PPD, 35.7% also reported symptoms of antenatal depression. Out of 3921 (7.7%) women who reported smoking during pregnancy, 32.6% smoked at high intensity (≥10 cigarettes/day) in all three trimesters and 36.6% had symptoms of antenatal depression. The main effect of PPD was the strongest for women who smoked at high intensity throughout pregnancy (aRR 1.65; 95% CI: 1.63, 1.68). A synergistic interaction was detected, and the effect of all maternal smoking patterns was augmented, particularly in late pregnancy for Increasers and Reducers.
Conclusion
Strong associations and interaction effects between maternal smoking patterns and co-occurring antenatal depression support smoking prevention and cessation interventions during pregnancy to lower the likelihood of PPD.
Data Sharing Statement
A PRAMS analytic data set is available to researchers upon request from the CDC after completion of a short application with a brief research proposal summary.
Acknowledgment
The authors would like to thank the Pregnancy Risk Assessment Monitoring System (PRAMS) Working Group members for coordinating collection of the data used in this analysis.
Disclosure
Dr Jennifer Barkin has a copyrighted (but not patented) instrument (the Barkin Index of Maternal Functioning) that is broadly relevant to maternal child health. The authors report no other conflicts of interest in this work.