Selective serotonin re-uptake inhibitor use during pregnancy: association with offspring birth size and gestational age

Background: Depression around the time of pregnancy affects at least 1 in 8 women and treatment with selective serotonin re- uptake inhibitors (SSRIs) in pregnant women has been increasing, but research on adverse effects on the fetus have so far commonly used designs unable to account for confounding. We aimed to examine the effects of prenatal SSRI exposure on offspring size outcomes and gestational age, and disentangle whether associations observed were due to the medication or other factors. Methods: We used a Swedish population-based cohort of 392 029 children and national registers to estimate the associations between prenatal exposure to SSRIs and depression on the outcomes birthweight, birth length, birth head circumference, gestational age at birth and preterm birth. A sub-sample of 1007 children was analysed in a within-family design that accounts for unmeasured parental genetic and environmental confounders. Results: Crude analyses revealed associations between prenatal SSRI exposure, and offspring birth size and gestational age. However, in the within-family analyses, only the association between SSRI exposure and reduced gestational age (-2.3 days; 95% confidence interval -3.8 to -0.8) was observed. Conclusions: This study indicates that prenatal SSRI exposure may not be causally related to offspring birth size. Rather, our analyses suggest that the association could be caused by other underlying differences instead of the medication per se. A small reduction of gestational age was associated with SSRI exposure in the within-family analysis and could be due to either the exposure, or other factors changing between pregnancies.