Women with myasthenia gravis (MG) have an increased risk of complications and adverse pregnancy outcome. This study has examined if this is true also for asymptomatic MG. Using data from the Medical Birth Registry of Norway, births of women prior to receiving an MG diagnosis or in complete clinical MG remission were compared with all non-MG births in Norway in the same period (1967-2000). Forty-nine births occurred in 37 women, 11 of them in clinical remission, and six thymectomized. The perinatal mortality was increased (P = 0.02) and induction of birth (P = 0.007) occurred more frequently. Protracted labor occurred more frequently in the target group (P = 0.03). One of the three children that died had Potter's syndrome. Both mothers with children who died were in complete clinical MG remission. One had previously given and one subsequently gave birth to a child with neonatal MG. The results indicate that complications in birth and pregnancy are not only related to clinical MG disease severity but to the underlying immunological dysfunction.