Clinical characteristics of pregnancies complicated by congenital myotonic dystrophy

OBJECTIVE Although the conventional prevalence of myotonic dystrophy is 1:8,000, the prevalence in Korean population was recently reported as 1:1,245. With higher domestic result than expected, we aimed to investigate the clinical characteristics of pregnancies complicated by congenital myotonic dystrophy in our institution. METHODS We have reviewed 11 paired cases of neonates diagnosed with congenital myotonic dystrophy and their mothers between July 2004 and May 2014, with clinical features including maternal history of infertility, prenatal ultrasonographic findings, and neonatal outcomes. Cytosine-thymine-guanine (CTG) repeat expansion in the myotonic dystrophy protein kinase gene of both neonates and their mothers was also examined. RESULTS None of mother was aware of their myotonic dystrophy traits before pregnancy. History of infertility followed by assisted reproductive technology accounted for 57.1% (4/7). Distinctive prenatal ultrasonographic finding was severe idiopathic polyhydramnios (66.7%, 4/6) with median amniotic fluid index of 43 (range, 37 to 66). In 37.5% (3/8) cases, decreased fetal movement was evident during prenatal ultrasound examination. For neonatal outcomes, more than half (6/11) were complicated with preterm birth and the proportion of 1-minute Apgar score <4 and 5-minute Apgar score <7 was 44.4% (4/9) and 66.7% (6/9), respectively. Most of neonates were admitted to the neonatal intensive care unit (9/10) because of hypotonia with respiratory problems and there was one infant death. Median number of cytosine-thymine-guanine repeats in mothers and neonates was 400 (range, 166 to 1,000) and 1,300 (range, 700 to 2,000), respectively. CONCLUSION Our data suggest that severe idiopathic polyhydramnios with decreased fetal movement in pregnant women, especially with a history of infertility, requires differential diagnosis of congenital myotonic dystrophy.