NUMERICAL ANALYSIS OF THE NORMAL HUMAN ANTENATAL FETAL HEART RATE

Abstract

A numerical method for separation of the frequency components of the fetal heart rate and for identifying episodes of high or low variation was applied to 196 64-min ultrasound records in normal pregnancies during the the last half of gestation. Most variables of heart period variation increased with gestation, as did the incidence of accelerations. Before 35 wk, accelerations of .gtoreq. 14 beats/min did not occur in all records. Cyclic episodes of low and high (unreactive and reactive episodes), associated with rest-activity cycles, could be identified from 27 wk onwards. After 36 wk gestation the length of low variation episodes increased and the variation during these episodes fell. Near term, low variation episodes lasted up to 40 min. On scrutiny of fetal heart rate records for evidence of normality or otherwise, due account should be taken of gestational age.