Metamizole use during first trimester-A prospective observational cohort study on pregnancy outcome

The analgesic metamizole (dipyrone) is not recommended during pregnancy due to limited experience. In several countries, metamizole has no market authorization because of agranulocytosis as a rare but severe adverse effect. However, in others, metamizole is available and widely used as a pain reliever, and its use occurs also during pregnancy, often followed by fears of potential teratogenic risk.

This prospective observational cohort study compared pregnancy outcomes of 446 women exposed with metamizole in the first trimester with a randomly selected control cohort comprising 887 women not exposed to metamizole. Relevant data were obtained via structured questionnaires applied during the first trimester and 2 months after the expected date of birth between January 2000 and December 2015.

The rate of major birth defects (7/373, 1.9%) was not increased in the metamizole cohort (OR adjusted 1.15, 95% CI 0.4-3.5). The cumulative incidences for spontaneous abortions did not reveal a significant difference between the exposed (12.2%, 32/446) and comparison cohort (19.4%, 77/887) (HR adjusted 0.72, 95% CI 0.5-1.1). Elective terminations of pregnancy (ETOP), mostly for "social" reasons, were more frequent in the metamizole (12.5%, 45/446) than in the comparison cohort (9.4%, 50/887; HR adjusted 1.48, 95% CI 0.98-2.2).

Metamizole exposure in the first trimester does not seem to bear a substantial teratogenic risk. Our study results support reassurance in those instances where metamizole has been used during an unrecognized pregnancy or where its use appears indispensable.