Prenatal manifestations and perinatal outcomes in congenital myotonic dystrophy: clinical patterns and diagnostic implications.

OBJECTIVES: This work aims to characterize the clinical manifestations and diagnostic challenges associated with pregnancies affected by congenital myotonic dystrophy through a detailed case report of an individual seen in our center and a comprehensive case series overview. CASE PRESENTATION: A 33-year-old woman presented at 33 weeks-gestation with symptomatic severe polyhydramnios (AFI 55.2) and an otherwise uncomplicated prenatal course with no anomalies on ultrasound. She underwent amnioreduction, which initially revealed normal genetic testing results (46,XX karyotype and normal microarray). At 34 weeks, she underwent repeat cesarean delivery for new-onset non-immune hydrops fetalis. Because of the hydrops, severe hypotonia, and respiratory distress requiring intubation of the neonate, further genetic testing was performed and was positive for congenital myotonic dystrophy (1,880 CTG repeats in DMPK). This testing also indicated that the mother had >200 repeats, consistent with myotonic dystrophy type 1. CONCLUSIONS: Idiopathic polyhydramnios and non-immune hydrops fetalis, even in the absence of structural anomalies, should prompt consideration of neuromuscular conditions such as congenital myotonic dystrophy in the differential diagnosis.