Effect of oxytocin and oral prostaglandin E2 on uterine contractility and fetal heart rate patterns

Abstract

The incidnce of uterine contractility and of abnormalities of fetal heart rate (FHR) pattern was determined in a series of 2,834 monitored gravid women with singleton pregnancies producing mature infants in vertex presentation. Those subjected to uterotonic agents for induction or augmentation of lbaor had significantly more tetanic contractions, baseline hypertonus, and coupling of contractions. Similarly, significantly more variable and late FHR decelerations occurred in stimulated labors, and these were concentrated primarily in those receiving oxytocin. The overall incidence of FHR decelerations associated with the use of prostaglandin E2 (PGE2) was comparable to that encountered in unstimulated labor. The similarity between the contractions of spontaineous labor and those labors produced by PGE2 is noted.

PIP: Of the 3700 gravid women with singleton pregnancies producing mature infants in vertex presentation, 2834 had routine uterine contractility (UC) and fetal heart rate (FHR) monitoring, producing records sufficient enough for data analysis. The monitoring was done using Corometrics Models 101, 101A, and 101B FHR monitors and a Hewlett-Packard Model 8020A cardiotocograph. Tetanic contractions were observed in 10.4% of labors overall, and in 8.3% of unstimulated labors; these were observed significantly more often when a uterotonic agent was used, totaling 14% of 1047 cases (t=4.54; p0.001). The increase was statistically significant only in oxytocin-stimulated labors. Baseline hypertonus was seen in 9.9% of unstimulated labors and in 13.5% of those labors subjected to stimulation (t=2.83; p0.01). Again, statistical significance was achieved only with oxytocin administration. Coupling was observed in 15.4% of unstimulated labors, but fewer (14.2%) stimulated labors. The findings also showed that both tetanic and coupled contractions occurred more often with prostaglandin E2 (PGE2) than with oxytocin induction or oxytocin stimulation; a finding, however, which needs further investigation. Significantly, more variable and late FHR decelerations were also noted in stimulated labors, particularly in those receiving oxytocin. Use of oral PGE2 did not affect the incidence of either variety of moderate-plus-severe FHR decelerations. These findings clinically support the reported similarity between spontaneous and PGE2--induced contractions, and their inherent dissimilarity from those produced by oxytocin.