Pregnancy outcome after first-trimester exposure to metformin: A prospective cohort study.

The aim of this study was to evaluate the risk of major birth defects and spontaneous abortion after metformin use during the first trimester of pregnancy. We conducted an observational cohort study comparing pregnancies with metformin treatment during the first trimester with non-exposed women matched for BMI and year of enrolment. Pregnancies were prospectively ascertained in the German Embryotox pharmacovigilance database between 2004 and 2014. The study sample included 336 pregnancies with metformin exposure for PCOS and fertility disorders (56.8%), diabetes (25.9%) and insulin resistance (14.9%) and 1011 matched controls. Independent of the treatment indication, neither the rate of major birth defects (OR adjusted 0.58, 95% CI 0.3-1.3) nor of spontaneous abortions (HR adjusted 0.95, 95% CI 0.6-1.5) was significantly increased among metformin exposed. Our study supports the evidence that metformin does not carry a developmental risk for the fetus when used during the first trimester.