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

Abstract

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 risk (pH less than 7.20, pH less than 7.10) 13.4 and 1.6% respectively. The distribution of the Apgar-scores after 1 min was assessed: 0-3: 1.7%, 4-6: 5.4%, 7-10: 92.9%. The dependance of the time variables from parity was studied. Two samples (N1=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 (tau) were found between the variable time and actual pH in blood of the umbilical artery and vein as well as pCO2, BEECF and HbO2 in the umbilical vein. The association however is not very close and thus clinically not of great importance. The deltapH (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 assesses: The acidotic risk (pH less 7.2) was doubled: 14.5% (7.7%) and AV-differences of all variables were "opened" if cordcoilings were observed. Apgar scores were not significantly different. Moreover, the association between AV-differences of each parameter and the variable time was studied: it became evident that with passage of time AV-difference is "closed" (-0.052 AV DpH/60 min "final stage" of labour, N=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.

The effect of labor on the acid‐base status of the newborn

“…The importance of taking the full acid-base status into consideration instead of only the pH has also been acknowledged (8,14) and an acidosis with a metabolic component that develops secondarily to fetal hypoxia is thought to be of greater importance than an acidosis of mainly 'respiratory' type where an accumulation of CO 2 is predominant. One common belief has been that the shorter duration of labor achieved through AML was to the benefit of the fetus (13). Since this concept was presented it has, however, also been ascribed to have other advantages.…”

“…The concept of 'active management of labor' (AML) was presented by O'Driscoll and Meagher at the National Maternity Hospital in Dublin in the late 1960s and the intention of this policy was originally to shorten the duration of labor for the primiparous women and, by way of this, give them a more agreeable experience of labor (9). This is probably based upon the traditional concept that a long second stage is in itself dangerous to the fetus (15) and some studies have indeed shown that a longer duration of the second stage is associated with a lower umbilical artery pH (2)(3)(4)13). One common belief has been that the shorter duration of labor achieved through AML was to the benefit of the fetus (13).…”

Durée des efforts expulsifs : pousser n’est pas jouer. Réponse à l’article de C. Le Ray et F. Audibert

“…Ces deux forces augmentent la pression intra-amniotique jusqu'à des valeurs pouvant atteindre 250 mmHg qui diminuent les perfusions placentaire et funiculaire [6,7]. En effet, le foetus est soumis pendant cette phase d'expulsion aux forces précitées mais aussi aux forces mécaniques volontaires (efforts expulsifs).…”

“…Dans une étude rétrospective incluant 4081 femmes de toute parité et visant à analyser la relation entre la durée du second stade du travail et l'équilibre acidobasique, Roemer et al [6] ont conclu, en 1976, que ce stade ne devait pas excéder 45 minutes.…”

Alternative positions for childbirth—Part II: Second stage of labor

“…Table 1 summarizes the duration of second stage as reported by various investigators. The duration of the true length of second stage is of considerable clinical interest because fetal acidosis has been shown to become more pronounced the longer the time between complete dilatation and delivery 96–98,100–103 …”