Myotonic disorders represent significant risk in pregnancy due to their complexity and the risk of maternal and fetal complications. Care of these pregnancies requires detailed pre-conception counselling, close monitoring of mother and fetus during the pregnancy and a delivery and postpartum plan involving a multidisciplinary team approach. A case of a woman with myotonia congenita diagnosed in pregnancy is presented, the general principles of care of women with myotonic disorders discussed, and care of the specific conditions in pregnancy reviewed. Trial registration: Not applicable.