Mirtazapine exposure in pregnancy and fetal safety: A nationwide cohort study

To investigate the association between mirtazapine exposure in pregnancy and risk of specific adverse pregnancy outcomes.

A register-based nationwide cohort study was conducted including all registered pregnancies in Denmark from 1997 to 2016. Mirtazapine-exposed pregnancies were compared with mirtazapine unexposed pregnancies in a 1:4 ratio matched according to propensity scores. Outcomes were major congenital malformations analyzed using log binomial models, and spontaneous abortion, stillbirth and neonatal death analyzed using Cox proportional hazard regression.

From a source population of 1,650,649 pregnancies, the propensity score-matched cohort included 4475 pregnancies (895 mirtazapine exposed) in the analysis of major congenital malformations. The analyses of spontaneous abortion included 9 500 pregnancies (1900 mirtazapine exposed), and for the analyses of stillbirths and neonatal deaths 9725 (1 945 mirtazapine-exposed) and 4485 pregnancies (897 mirtazapine-exposed) were included, respectively. Thirty-one (3.5%) children were diagnosed with major congenital malformation among the mirtazapine exposed compared with 152 (4.3%) among the unexposed pregnancies (OR=0.81, 95% CI 0.55-1.20). Spontaneous abortion occurred in 237 (12.5%) of the mirtazapine exposed compared with 931 (12.3%) of the unexposed pregnancies (HR = 1.04%, 95% CI 0.91-1.20). The analyses revealed no increased risk of stillbirth (HR = 0.88%, 95% CI 0.34-2.29) or neonatal death (HR = 0.60%, 95% CI 0.18-2.02).

In this nationwide Danish register study, mirtazapine exposure in pregnancy was not associated with major congenital malformations, spontaneous abortion, stillbirth, or neonatal death. Clinicians and patients can be reassured that mirtazapine is safe in pregnancy.