The effect of pre-existing myasthenia gravis (MG) on delivery and the newborn was investigated in a retrospective study of 127 births by mothers with MG compared to 1.9 million births by mothers without MG at the University of Bergen, Norway. Women with MG have an increased risk of complications at delivery, especially the risk of premature rupture of amniotic membranes (5.5% vs 1.7%, p=0.001). Risk of cesarean sections doubled (17.3% vs 8.6%, p=0.001). Birth defects and/or neonatal complications occurred in 27 (21%) of the 127 children, and 5 (3.9%) had severe defects vs 1.9% in the reference group (NS). Three with severe defects died. Neonatal MG was diagnosed in 5 cases. Perinatal mortality was 2.4% in the MG group vs 1.4% in the reference group (p=0.7, NS). A comparison of 45 births in mothers previously thymectomized and 82 nonthymectomy MG births found no significant differences regarding delivery and birth complications or defects. 
COMMENT. MG is associated with an increased risk of complications during delivery and higher rate of ceasarean sections. A higher rate of birth defects and perinatal mortality in infants born to MG mothers is not significantly different from non-MG births. Prior thymectomy does not prevent the increase in delivery complications in MG mothers.