MYOTONIC-DYSTROPHY IS A SIGNIFICANT CAUSE OF IDIOPATHIC POLYHYDRAMNIOS

OBJECTIVE: Myotonic dystrophy, the most common form of muscular dystro phy seen in pregnant women, may be a significant cause of middle trime ster polyhydramnios. Our purpose was to determine the prevalence of my otonic dystrophy in women with idiopathic polyhydramnios and to charac terize the ultrasonographic findings associated with cases, STUDY DESI GN: We examined the cases of 67 patients who were delivered of infants at the University of Utah between 1992 and 1996 with a diagnosis of i diopathic polyhydramnios (amniotic fluid index >25). Women with diabet es mellitus, hydrops, or fetal anomalies known to cause polyhydramnios were excluded from the study. Amniotic fluid samples or cord blood sa mples were obtained from 41 patients, and polymerase chain reaction am plification and Southern blot analysis were performed to detect the pr esence of the myotonic dystrophy mutation. Ultrasonographic findings, prenatal course, and neonatal outcomes were reviewed in all cases. RES ULTS: Four of the 41 patients tested had the myotonic dystrophy mutati on, yielding a prevalence in our population of 9.7%. Three of the 4 pa tients reported a family history of myotonic dystrophy. Ultrasonograph ic findings associated with a positive result included abnormal postur ing of extremities (3/4) and unilateral clubbed foot (3/4). No other s tructural or growth abnormalities were seen. Two of the patients were delivered before term, 1 at 26 weeks and 1 at 32 weeks. Three of the 4 infants were severely affected, necessitating admission to the intens ive care unit, and 1 died on day 11 after birth. One infant, whose myo tonic dystrophy mutation consisted of between 800 and 900 triplet repe ats, did not require admission to the intensive care unit. CONCLUSION: Myotonic dystrophy may be seen as idiopathic polyhydramnios and shoul d be considered as part of the differential diagnosis in these cases. Women with a familial history of myotonic dystrophy or ultrasonographi c evidence of hypotonia, including positional abnormalities of the ext remities, should be offered deoxyribonucleic acid testing for the myot onic dystrophy mutation.