FHR variability and other heart rate observations during second stage labor.

Seventy-four fetal heart rate (FHR) records that were continued to vaginal delivery were selected for study from more than 2000 intrapartum FHR tracings. Thirty-six of the births were associated with neonatal depression and Apgar scores of 3 or less and/or 6 or less at 1 and 5 minutes, respectively; 38 patients exhibited normal Apgar scores (7 and 10 at 1 and 5 minutes, respectively). Twenty minutes of heart rate activity immediately prior to birth was the basis of analysis. All categories of loss of short-term beat-to-beat variability (BBV), both baseline and with decelerations, were observed more frequently in the group with low Apgar scores (P less than .001). In assessing variability, duration of observed loss of BBV appears to be an extremely critical factor. If BBV was lost 50% or less of observation time, a wide range of Apgar scores was observed. When more than 50% of the record showed loss of BBV, the number of depressed neonates was relatively high. Bradycardia (heart rate of less than 120 beats per minute) was present frequently in the records of the normal group. The number of variable decelerations and the amount of uterine activity were relatively high during second stage labor; a similar frequency was noted in both groups. Decelerations were nearly uniformly associated with uterine contractions in both groups, and accelerations were also noted in both groups. Uniform decelerations (late) were also present in both groups, with a greater frequency in the group with lower Apgar scores, but there were no distinguishing characteristics noted.