Fetal heart rate patterns in labors with intact and with ruptured membranes.

In previous papers [l, 6] it was reported that the rupture of membranes facilitates the production of type I dips in the fetal heart rate (FHR) tracing. This Statement is based on the effect of amniotomy on FHR records [6] and also on the quantitative study of a group of 26 monitored labors induced with oxytocin [1], in which membranes were artificially ruptured when cervical dilatation was between 4 and 6 cm: The incidence of type I dips was significantly higher after amniotomy than before this procedure. The type I dips recorded after rupture of the membranes were attributed to the uneven compression and deformation of the fetal head, or to occlusion of the umbilical vessels during uterine contractions [l, 6,19]. It was postulated that both effects of uterine contractions were facilitated by the rupture of the bag of waters and corresponding loss of amniotic fluid around the fetal head or the umbilical cord. The design of this previous study [1] did not allow the analysis of the effects of amniotomy independently from the influence of the engagement of the fetal head in the pelvis. The head was usually not engaged from the beginning of labor until the time of amniotomy, whereas it was engaged during most of the period elapsing after rupture of membranes until delivery. Since engagement increases the pressure received by the fetal head during uterine contractions [11,19), it may facilitate the production of type I dips. The present study was designed prospecCurriculum vitae