Risk of Myasthenia Gravis Exacerbation During Pregnancy and Postpartum: A Nationwide Cohort Study.

BACKGROUND AND

objectivesThe impact of pregnancy on the clinical course of myasthenia gravis (MG) remains uncertain, with existing evidence mainly derived from small case series. Using nationwide longitudinal register data, we aimed to assess the risk of MG exacerbation during pregnancy and up to 1 year postpartum.

methodsIn this population-based cohort study, we included women with MG recorded in the Swedish National MG Register who had singleton pregnancies documented in the Medical Birth Register after MG diagnosis (1987-2019). The exposure was pregnancy, and the outcome was MG exacerbation. The primary outcome measure was hospital admissions with MG during pregnancy and the postpartum year, compared with the year preceding pregnancy. Cox proportional hazards models estimated hazard ratios (HRs), adjusting for disease duration and prior thymectomy. The secondary outcome measure was changes in immunosuppressive MG medications during pregnancy and postpartum.

resultsWe identified 112 women with MG (median age 30 years) with 176 singleton pregnancies. During pregnancy, women were not more likely to be hospitalized for MG than in the prepregnancy year (HR 0.74, 95% CI 0.39-1.41), and there was no increased risk of longer hospital admissions (HR 0.83, 95% CI 0.36-1.88). The postpartum period was associated with an increased risk of prolonged MG admissions during the first 3 months (HR 5.02, 95% CI 1.66-15.24), with a similar risk observed throughout the first 12 months postpartum (HR 4.52, 95% CI 1.26-16.14). During pregnancy, immunosuppressive MG medications were reduced or discontinued in 13 pregnancies and increased in 6. Postpartum, medications were initiated or escalated in 10 pregnancies and reduced in none. The risk of prolonged MG admissions was higher in periods outside of pregnancy compared with the prepregnancy year (HR 2.95, 95% CI 0.84-10.43), suggesting that women conceive during periods of relative disease stability. DISCUSSION: Pregnancy was not associated with an increased risk of MG exacerbation. The postpartum period was linked to more severe or prolonged exacerbations in a minority of women, highlighting the importance of close monitoring after delivery. Milder exacerbations not requiring hospitalization or clear medication escalation may have been underestimated, underscoring the need for larger prospective international studies that include detailed clinical data.