Congenital myotonic dystrophy: An overlooked diagnosis not amenable to detection by sequencing.

Congenital myotonic dystrophy should be a consideration for cases of severe polyhydramnios identified by ultrasound. Myotonic dystrophy is detected using PCR and southern blot and is not typically included on next generation sequencing (NGS) panels that test for similar conditions. Clinicians should consider more specialized genetic testing than microarray and NGS in these cases.