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

Abstract

Latin American Center of Perinatology and Human DevelopmentMontevideo, UruguayReceived: April 2, 1973. Accepted May 16, 1973In previous papers [l, 6] it was reported that therupture of membranes facilitates the produc-tion of type I dips in the fetal heart rate (FHR)tracing. This Statement is based on the effect ofamniotomy on FHR records [6] and also on thequantitative study of a group of 26 monitoredlabors induced with oxytocin [1], in which mem-branes were artificially ruptured when cervicaldilatation was between 4 and 6 cm: The incidenceof type I dips was significantly higher afteramniotomy than before this procedure. The typeI dips recorded after rupture of the membraneswere attributed to the uneven compression anddeformation of the fetal head, or to occlusionof the umbilical vessels during uterine con-tractions [l, 6,19]. It was postulated that botheffects of uterine contractions were facilitated bythe rupture of the bag of waters and corre-sponding loss of amniotic fluid around thefetal head or the umbilical cord. The designof this previous study [1] did not allow the ana-lysis of the effects of amniotomy independentlyfrom the influence of the engagement of the fetalhead in the pelvis. The head was usually notengaged from the beginning of labor until thetime of amniotomy, whereas it was engagedduring most of the period elapsing after ruptureof membranes until delivery.Since engagement increases the pressure receivedby the fetal head during uterine contractions[11,19), it may facilitate the production of type Idips. The present study was designed prospec-