Is End-Stage Deceleration of the Fetal Heart Ominous?

Abstract

Little information is available on the significance of the dramatic fall in fetal heart rate which may occur during the second stage of labor. Although the drop appears ominous, the newborn infant is usually in excellent condition. In the present study, an attempt is made to assess the significance of end-stage deceleration and to discuss the management of labor in such cases. During the period from January 1 to July 1, 1980, 3540 women gave birth in the authors' medical center, and 1593 (45 per cent) had continuous fetal heart rate monitoring in labor. End-stage deceleration was diagnosed in 55 (3.4 per cent) of those monitored. The average drop in baseline fetal heart rate during end-stage deceleration was 45.5 beats per minute (range, 20 to 90 beats per minute). Forty-nine of the infants had one-minute Apgar scores of 7 or more; the remaining six were depressed at delivery and had one-minute Apgar scores of 5 or less. In 49 patients who had healthy babies, the fetal heart rate pattern preceding deceleration was normal. In the six patients who gave birth to depressed babies, pathological fetal heart rate patterns were present before deceleration, although fetal scalp blood pH in early labor was within normal limits. In four of these six, fetal scalp blood was sampled again during end-stage deceleration, and the pH was significantly lower. Vacuum extractor or outlet forceps were used in five deliveries; the sixth fetus was delivered spontaneously 5 minutes after the onset of deceleration, severely depressed and acidotic. Umbilical vein pH values in all six babies were acidotic. No relation was found between the depth of drop in fetal heart rate or the duration of deceleration and fetal condition on delivery, provided the heart rate was normal until end-stage deceleration. When umbilical vein pH values were related to the duration of deceleration, however, it was shown that values dropped to pre-acidotic levels when deceleration had persisted for more than 15 minutes (P < 0.001). The mean pH was 7.27 when end-stage deceleration lasted 1 5 minutes or less and 7.23 if deceleration persisted for more than 1 5 minutes (P < 0.001). Umbilical vein pH and the one-minute Apgar score were less dependent on the mode of delivery than on fetal heart rate patterns during labor and the duration of deceleration. Fetal scalp blood pH during end-stage deceleration was obtained from 25 patients and compared with umbilical vein blood pH. A weak correlation between the two could be demonstrated (r = 0.354), but all four infants who had low fetal scalp blood pH values during deceleration also had preacidotic or acidotic umbilical vein blood pH values.