Evaluation of fetal heart rate in relation to the intrauterine 20 mm Hg level.

The purpose of the author's study was to investigate whether any changes in fetal heart rate (FHR) and in fetal acid-base status could be observed when the intrauterine pressure rises above 20 mm Hg. 16 primigravidae were studied. In 11 out of 16 patients labor was induced by amniotomy, in 9 cases oxytocin was given, and in 12 patients pethidine and promethazine (Phenergan) was administered. Two new parameters were introduced into the study of the collected material: the peak variation in FHR (bpm) i.e. the difference between the highest and lowest FHR over a given period of time; the contraction energy, i.e. the product of duration and intensity of intrauterine contractions as measured from the 20 mm Hg level. In 15 out of 16 women the mean peak variation in FHR was highest during a uterine contraction (greater than 20 mm Hg). After a uterine contraction (less than 20 mm Hg) the mean peak variation did not immediately return to control values. It is suggested that in the 16 patients studied, the increase in FHR peak variation during uterine contraction is basically caused by a slight transient fetal hypoxia, exaggerated during the expulsion period of labor by cord entanglement.