Indomethacin and amniocentesis-induced changes in fetal flow velocity waveforms

The effect of genetic amniocentesis on flow velocity waveforms in the fetal aorta and the umbilical artery, and fetal heart rate and their correlation with uterine contractions was examined in 75 pregnant women who underwent this procedure. Forty-three were untreated and 32 were pretreated with indomethacin. Median maternal age was 36 years and median gestational age was 18 weeks. The resistance index of waveforms from the fetal aorta was stable at 0.8 throughout the approximately 20-h study period in both groups, but the systolic/diastolic ratio in the umbilical artery increased significantly after amniocentesis in the untreated group, and remained stable in the treated group. Fetal heart rate remained at about 150 beats/min throughout all measurements in both groups. These findings indicate that genetic amniocentesis causes an increase in downstream resistance in the umbilical artery which, however, remains within normal limits. This mild fetoplacental response to amniocentesis can be suppressed by the administration of a potent prostaglandin inhibitor like indomethacin.