Observational cohort finds uncertain fetal risk after first-trimester JAK inhibitor exposure

An observational analysis of 44 pregnancies with first-trimester exposure to Janus kinase inhibitors found two major congenital anomalies among 32 live births, alongside five spontaneous abortions and seven elective terminations. The pregnancies were prospectively enrolled in the German Embryotox database between January 1, 2017, and November 15, 2025, and then analyzed as observational data. Exposure involved baricitinib in 17 pregnancies, filgotinib in three, tofacitinib in eight and upadacitinib in 16.

Of the 44 exposed pregnancies, 32 resulted in live births. Two babies were born with major congenital anomalies: one ventricular septal defect and one hypospadias. This amounts to 2 of 32 live births, or 6.3%.

Five pregnancies ended in spontaneous abortion, including one case of fetal anencephaly, and seven pregnancies were terminated electively. These small numbers document observed outcomes but cannot determine whether JAK inhibitor exposure caused the anomalies or pregnancy losses. Neonatal assessments among the live births identified two preterm births at 36 weeks’ gestation, three infants small for gestational age and two newborns large for gestational age.

The authors concluded that current evidence is insufficient to establish or exclude an association between JAK inhibitor exposure and adverse fetal outcomes. They stated that potentially harmful effects cannot yet be ruled out, that routine use during pregnancy is not recommended, and that treatment should be approached with caution and a critical risk-benefit assessment until more data are available.

Subject of Research: Pregnancy outcomes following first-trimester exposure to JAK inhibitors

Article Title: Pregnancy outcome after first-trimester exposure to JAK inhibitors – an evaluation of the German Embryotox cohort

Article References: Habbel, A.-S., Beck, E., Mueller, A., & Dathe, K. (2026). Pregnancy outcome after first-trimester exposure to JAK inhibitors – an evaluation of the German Embryotox cohort. BMC Pharmacology and Toxicology. https://doi.org/10.1186/s40360-026-01263-4

Image Credits: AI Generated

DOI: 10.1186/s40360-026-01263-4

Keywords: JAK inhibitors, pregnancy safety, first-trimester exposure, congenital anomalies, fetal risk, baricitinib, upadacitinib, tofacitinib, filgotinib, German Embryotox, Pregnancy, outcome