Early decelerations of the fetal heart rate from occlusion of the umbilical cord

Analysis of fetal deaths prior to the onset of labor at the Maternidad "Santa Cristina during the period from June 1972 to September 1974 suggested that cord complicationswere the probable cause of death in 62% of the cases. Similar findings have been reported by other centers [3,18,21]. In an attempttoreduce this number of antepartum fetal deaths we decided to monitor the fetal heart rate in patients admitted prior to labor (during the first 24 hours after admission). A decrease in the fetal heart rate resembling the pattern of early deceleration or type I dip was frequently seen. It is currently believed that this heart rate pattern is caused by compression of the fetal head during uterine contractions [l, 5, 11, 13, 15, 19], This belief is based on clinical observations and experiments in human fetuses [l, 15]. At the time our patients were monitored, most had intact membranes and the fetal head was not engaged, or the presentation was by breech, making it very unlikely that the fetal head could be compressed during a uterine contraction.We therefore embarked on a search for an alternate explanation for these changes in fetal heart rate. The fetal heart rate pattern associated with cord compression has been described as 'Variable' [11, 13]. This description alludes mainly to the different shape of successive decelerations (for their different amplitude and/or duration) as well as to the different time relationships between the onset of the contraction and the corresponding deceleration [5, 11, 13]. The variability of this pattern, when typical, is easily recognized over periods of 15 to 30 minutes of continuous recording. In our patients monitored during late pregnancy, this Variable" pattern was relatively infrequent. On the contrary, early decelerations following a rather non-variable pattern, were often seen in fetuses who later evidenced cord complications at birth. This suggested that compression of the umbilical cord might be causing the heart rate patterns which we were observing.Otherauthors have also proposed that early decelerations or type I dips could be related to compression of the umbilical cord [5,22] or to other unknown factors [20]. In order to explore this possibility in greater detail we have analyzed the heart rate changes, in a selected group of patients during the late antepartum period, and related these to the presence or absence of umbilical cord complications at birth.