Fetal heart rate response to amniocentesis in early pregnancy

Fetal heart rate (FHR) was studied during 14 consecutive amniocenteses in the 15th to 16th week of gestation by means of an ultrasound FHR monitor making beat to beat registration. FHR was monitored for 15 min prior to amniocentesis and 30 min after the procedure. The amount of fluid aspirated varied between 20 and 30 ml. In seven amniocenteses the fetuses reacted with reduced fetal heart rate variability, "silent pattern". The beat to beat variation fell from a level of 15-20 beats per min to 0-1 beat per min, starting four minutes after the amniocentesis, and lasting for two minutes. This pattern was never seen in the baseline study periods prior to amniocentesis (p < 0.01). The most likely explanation for this new observation seems to be that some fetuses are influenced by the reduction of amniotic fluid and stay immobile for some time.