Is polyhydramnios in an ultrasonographically normal fetus an indication for genetic evaluation?

Objective: Our purpose was to determine the frequency of fetal chromosomal anomalies in pregnancies complicated by polyhydramnios.
Study Design: Between Jan. 1, 1992, and July 31, 1993, an amniotic fluid index was measured prospectively in 2730 third-trimester pregnant women. Polyhydramnios was defined as an amniotic fluid index > or = 24 cm. A computer search identified all infants born with structural or chromosomal anomalies.
Results: Polyhydramnios was detected in 49 of 2730 women (1.7%). The incidence of chromosomal anomalies was two in 49 (4.1%) compared with three in 2681 (0.12%) among women with normal fluid (p < 0.05). Six of the 49 newborns had structural anomalies (12.2%), whereas 48 of 2681 (1.8%) structural anomalies occurred in the control group (p < 0.05). Among study patients both fetuses with chromosomal anomalies were growth retarded; four of the six structural anomalies were associated with an amniotic fluid index > 30 cm.
Conclusions: (1) Polyhydramnios is associated with an increased incidence of congenital fetal anomalies. (2) Growth-retarded fetuses with polyhydramnios warrant genetic evaluation. (3) A genetic study is not absolutely indicated for patients with polyhydramnios and a sonographically normal fetus.