Risk of fetal chromosomal abnormalities in idiopathic polyhydramnios.

BACKGROUND

Polyhydramnios is often associated with fetal anatomical abnormalities; thus chromosome analysis is indicated for fetuses with those indications. However, chromosome analysis for patients with idiopathic polyhydramnios is often overlooked. This is an attempt to evaluate the necessity for chromosome analysis in pregnancies with idiopathic polyhydramnios.

METHODS

Genetic amniocentesis or percutaneous umbilical blood sampling was done in 33 cases with idiopathic polyhydramnios which appeared at 26 to 34 weeks' gestation. To exclude false idiopathic polyhydramniotic cases, a level II sonographic examination was carefully performed for those fetuses with abnormal chromosome. Autopsy ultrasound examination and X-ray examination were done in four neonates with abnormal karyotypes, and the results were compared with prenatal sonographic findings.

RESULTS

Seven (21.2%) out of the 33 cases were, surprisingly found to have chromosomal abnormalities. Three out of the seven cases were diagnosed to have fetal anatomical defects, at a repeated level II sono-graphic examination. The incidence of fetal chromosome abnormalities in idiopathic polyhydramnios was 13.3% (4/30). After 7 cases of women older than 34 years and 3 cases with false idiopathic polyhydramnios were excluded, the incidence of chromosomal abnormalities in pregnancies of those under 34 years of age with idiopathic polyhydramnios was 8.3% (2/24).

CONCLUSIONS

According to the results of this study and other papers, the incidence of chromosomal abnormalities in fetuses with idiopathic polyhydramnios is much higher than that for maternal age specific risk at 34 years of age. Therefore fetal chromosome analysis for pregnancies with idiopathic polyhydramnios is recommended to avoid unnecessary Cesarean sections and deliveries of viable babies with abnormal chromosomes.