Response of Fetal Acid—Base Balance to duration of Second Stage of Labour

Abstract

Roemer, V. M., Harms, K., Buess, H. and Horvath, T. J. (Dept. of Obstetrics and Gynaecology, University of Tübingen, Tübingen, West Germany and University of Basel, Basel, Switzerland). Response of fetal acid–base balance to duration of second stage of labour.Int J Gynaecol Obstet 14: 455–471, 1976.Data from 4081 vaginal deliveries (no caesarean sections) were analyzed retrospectively (IBM 730/158) with regard to duration of second and “final stage” of labour and fetal outcome (acid–base balance and Apgar scores). The average duration of the two periods amounted to 22.8±29.6 and 9.9±7.8 min. Mean pH (UA) was 7.268±0.084 and the acidotic risks (pHN₁= 1755, N₂=1098) of uncomplicated term pregnancies were chosen according to 7 clinical selection criteria differing only in the presence of cord entanglements at birth. The association between the two time variables and parameters of the fetal acid–base balance in cord blood was evaluated using rank correlation‐ and polynomial regression analysis. Highly significant correlations (τ) were found between the variable time and actual pH in blood of the umbilical artery and vein as well as pCO₂, BE_ECF and HbO₂ in the umbilical vein. The association however is not very close and thus clinically not of great importance. The ΔpH (UA & UV) pro 60 min of second (and “final”) stage of labour was computed and amounted to −0.024 (−0.087) in blood of the umbilical artery and −0.036 (−0.115) in blood of the umbilical vein and −0.017 (−0.062) (UA) and −0.032 (−0.120) units (UV) in the sample with and without apparent cord entanglements at birth respectively. The response of fetal acid–base balance to cord compression during second stage of labour was assessed: The acidotic risk (pHN=1098) indicating time related impairment of placental function. From these observations and data of the literature the conclusion is drawn that second stage of labour should not exceed 45 min in any patient. Furthermore it is concluded that in cases without signs of impending fetal distress it seems to be possible to wait more than 20 (Multipara) or 30 min (Primipara) duration of “final stage” without increased risk of fetal peril measured in terms of acidemia and clinical depression. This is valid only in term pregnancies with the possibility of continuous monitoring of FHR, in cases with normal uterine activity, uneventful course of first stage of labour and cooperative, vigorous patients. The indications for termination of delivery by vaginal operations in cases without impending fetal distress are discussed.