Risk of pregnancy loss in patients exposed to mycophenolate compared to azathioprine: A retrospective cohort study.

PURPOSE: To evaluate the relative risk of pregnancy loss associated with mycophenolate (MPA) vs azathioprine (AZA) use.

METHODS

We conducted a retrospective cohort study using the IBM MarketScan Research Databases (2005-2015). Patients with ≥1 MPA or AZA prescription claim during the first trimester were included. The study outcome was pregnancy loss (spontaneous abortion or stillbirth). Potential confounders included age, drug indications, comorbidities, other teratogenic medication use, and gestational age at first MPA or AZA prescription fill. The risk for pregnancy loss was estimated using a generalized estimating equation model with stabilized inverse probability of treatment weighting. In sensitivity analyses, we varied the exposure definition, outcome definition, and the analytical method.

RESULTS

Among 111 pregnancies exposed to MPA, 55 resulted in pregnancy loss (49.5%). Among 471 pregnancies exposed to AZA, 113 had pregnancy loss (24.0%). The unadjusted relative risk for pregnancy loss was 2.0 (95% CI 1.6, 2.6), and the adjusted relative risk was 1.9 (95% CI, 1.6, 2.3) compared to AZA. Relative risk estimates were stable in all sensitivity analyses.

CONCLUSION

Exposure to MPA during early pregnancy was associated with a 2-fold increase in pregnancy loss risk.