The effect of the duration of the second stage of labour on the acid-base state of the fetus

A prospective study was made in 153 patients with a second stage of labour lasting 1 to 120 min. Maternal venous, umbilical artery and vein blood were analysed for acid-base variables and lactate levels. Blood was obtained immediately at delivery. Fetal heart rate monitoring data and blood test results were related to the duration of the second stage of labour and clinical outcome. In primiparae and multiparae there was a steady rise in umbilical artery lactate levels, with duration of second stage of labour, P less than 0.025 and P = 0.023, respectively. The median umbilical artery pH decreased significantly from 7.31 in patients with a second stage of labour that lasted less than or equal to 15 min to a pH of 7.25 in patients with a second stage of labour that lasted more than 30 min. Changes in PO2 and PCO2 were not statistically significant.     

The effect of intravenous ritodrine on the acid-base status of the fetus during the second stage of labour.

A progressive fetal respiratory acidosis occurs in the second stage of labour. A double-blind controlled trial showed that the intravenous infusion of Ritodrine abolished this.     

The second stage of labour

This is the third 'midwifery basics' series aimed at student midwives, and focuses on midwifery care during labour. This month, we look at care during the second stage of labour. Students are encouraged to seek further information through a series of activities, and to link theory with practice by considering the issues relating to the care of the woman described in the vignette.     

Response of fetal acid--base balance to duration of second stage of labour.

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.     

Uterine activity in the second stage of labour and the effect of epidural analgesia

Summary. Uterine activity was measured during the second stage of normal labour in 20 patients with and 31 patients without epidural analgesia. There was a significantly lower uterine activity integral (UAI) in patients having epidural analgesia, and it is suggested t h a t this may contribute to the increased rate of instrumental delivery associated with epidural analgesia.     

Uterine activity in the second stage of labour and the effect of epidural analgesia

Uterine activity was measured during the second stage of normal labour in 20 patients with and 31 patients without epidural analgesia. There was a significantly lower uterine activity integral (UAI) in patients having epidural analgesia, and it is suggested that this may contribute to the increased rate of instrumental delivery associated with epidural analgesia.     

The accuracy of fetal pulse oximetry in the second stage of labour

The aim of this study is to assess the accuracy of fetal monitoring with pulse oximetry at delivery. The pulse oximetry reading from the fetus at delivery was compared to fetal condition at birth. There is poor correlation between fetal scalp oximetry readings at delivery and fetal condition (Apgar scores), umbilical venous or arterial blood gas analysis or pH. Although there are good theoretical reasons why the correlation should not be perfect, the wide deviation from expected values suggest that readings taken during delivery are particularly prone to errors. Examination of the unprocessed photodetector signal during the second stage of labour reveals considerable movement interference. The signal may also be affected by congestion and transmitted venous pulsation in the scalp as the head crowns. The current generation of reflectance pulse oximeters can predict fetal hypoxemia during labour but a single reading during delivery is subject to too much movement interference to produce useful data.     

Failure to progress in the second stage of labour.

Spontaneous vaginal delivery without obstetric intervention remains the goal for most pregnant women. Midwives and obstetricians aim to support women in achieving this result, which is associated with the lowest risk of morbidity for both mother and baby. Despite the best efforts of the labouring woman and her carers, some women will fail to progress in the second stage of labour, and obstetric intervention will be required. This review evaluates recent data addressing the diagnosis, aetiology and management of failure to progress in the second stage of labour, and explores aspects of maternal and neonatal morbidity associated with this event.     

The association between neonatal head circumference and second stage duration

Abstract

Purpose: To determine if head circumference (HC) is an independent factor influencing second stage duration stratified by parity and epidural use.

Materials and methods: A retrospective cohort analysis of all live, singleton, term (37–42 weeks) vaginal deliveries in one university affiliated medical center (2012–2014). Exclusion criteria included operative deliveries due to fetal distress, major fetal anomalies/chromosomal abnormalities or cases with missing anthropometric data. Maternal demographics, labor characteristics and neonatal anthropometrics including birth weight and HC were retrieved. Multivariate linear regression was utilized to evaluate the association between HC and second stage duration. Analysis was stratified into four groups by parity and epidural use.

Results: Of the 16 240 singleton vaginal deliveries during study period, 12 428 deliveries met inclusion criteria. Stratification by parity and epidural analgesia yielded four groups: 3337 (26.9%), 735 (5.9%), 5099 (41.0%) and 3257 (26.2%) deliveries – nullipara with/without epidural and multipara with/without epidural, respectively. In all groups, a large neonatal HC was significantly and independently associated with longer second stage duration: nullipara with epidural (beta 10.06, 95% CI 7.75–12.37), nullipara without epidural (beta 7.58, 95% CI 4.73–10.43), multipara with epidural (beta 4.64, 95%CI 3.47–5.8) and multipara without epidural (beta 1.35, 95% CI 0.76–1.94), p?<?.001 for all. Birth weight was not associated with second stage duration in any of the groups (p?>?.05).

Conclusion: Large neonatal HC is significantly associated with longer second stage duration.     

The effect of labour on prolactin and cortisol concentrations in the mother and the fetus

Concentrations of prolactin and cortisol were determined in maternal and umbilical cord serum of women delivered by elective Caesarian section and by vaginal delivery. There was no difference in the concentration of prolactin in the two groups of women. Similarly, cord blood prolactin concentrations were not significantly different in the two groups. Cortisol concentrations in the women undergoing Caesarian section were similar to the vaginal delivery group before the onset of labour. However, there was a significant increase in cortisol concentration at delivery following labour. The cord blood cortisol concentration was significantly higher in the neonates delivered vaginally, and it correlated with the maternal cortisol concentration at delivery. The relevance of these findings is discussed.     

Fetal transcutaneous carbon dioxide tension during the second stage of labour

Fifteen women were studied during the second stage of labour by measuring simultaneously fetal transcutaneous carbon dioxide tension (Tc PCO2 and maternal end-expiratory PCO2. A linear increase of Tc PCO2 with time was observed, predominantly because of changing maternal respiration patterns. The degree of maternal hyperventilation had no adverse effect on the status of the newborn infant.     

Fetal transcutaneous carbon dioxide tension during the second stage of labour

Summary. Fifteen women were studied during the second stage of labour by measuring simultaneously fetal transcutaneous carbon dioxide tension (Tc Pco₂ and maternal end-expiratory Pco₂ . A linear increase of Tc Pco₂ with time was observed, predominantly because of changing maternal respiration patterns. The degree of maternal hyperventilation had no adverse effect on the status of the newborn infant.