Myotonia dystrophica: obstetric complications.

We describe the course and outcome of 23 pregnancies in six women affected by myotonia dystrophica in a large Labrador family. A seventh patient had 14 pregnancies, so that the infertility commonly described in this disorder did not apply to this family. The rate of complications was high, particularly in respect of polyhydramnios, premature onset of labor, cesarean section, postpartum hemorrhage, and neonatal deaths. Polyhydramnios indicated that the fetus was abnormal. Direct observation of an atonic uterus at cesarean section supported other evidence that uterine muscle may be affected. We also report a newborn infant with the congenital form of myotonic dystrophy, a manifestation which has been attributed to the effect of a maternal intrauterine factor upon a fetus carrying the gene.