Abstract
Background
Friedman found in 1955 that most nulliparous women without epidural analgesia delivered within two hours in second stage of labor. Estimating the probability of spontaneous delivery and assessing relevant predictors in a contemporary obstetric population is essential for clinical decision making.
Objective
The aim of this study was to estimate the probability distribution of spontaneous delivery in occiput anterior and occiput posterior position during the pushing phase, stratified by parity and epidural analgesia.
Study Design
The study was a retrospective cohort study at three Norwegian University hospitals from 2012-2024. Women who reached the active second stage of labor and delivered a single fetus in cephalic presentation at term were eligible. The primary outcome was the estimated duration from start of the pushing phase to spontaneous delivery. Fetal position was classified as occiput anterior or occiput posterior at time of delivery. Secondary outcomes were adverse maternal (obstetric anal sphincter injuries and post-partum hemorrhage >1000 ml) and neonatal outcomes (five minutes Apgar score <7 and umbilical cord pH <7.0).
The data were analyzed with survival methods.
Results
The final study population comprised 120 218 births. Among nulliparous women, there were 50 972 (94.8%) births in occiput anterior position and 2798 (5.2%) in occiput posterior position. Corresponding values among parous women were 63 153 (95.0%) and 3295 (5.0%), respectively.
The estimated probability of spontaneous delivery within 120 minutes in nulliparous women with occiput anterior delivery was 98.4% (95% confidence interval 98.1-98.6) in women without epidural and 84.3% (83.1-85.4) in women with epidural analgesia. The benefit of pushing more than 120 minutes in women without epidural was marginal, whereas an additional 30 minutes of pushing increased the probability to 90.1% (86.3-92.8) in women with epidural.
In nulliparous women with occiput posterior deliveries the corresponding probabilities after 120 minutes were 78.6% (73.4-82.8) in women without epidural and 44.9% (40.5-49.0) in women with epidural. Few spontaneous deliveries occurred after 120 minutes and the benefit of pushing beyond 120 minutes for nulliparous women with persistent occiput posterior position was low.
In parous women with occiput anterior deliveries, the probability of spontaneous delivery after 60 minutes pushing was 99.0% (98.9-99.1) in women without epidural analgesia and 94.5% (94.1-94.9) in women with epidural. Women without epidural did not benefit from pushing more than 60 minutes, whereas the probability increased to 97.4% (97.0-97.7) after 90 minutes in women with epidural. The probabilities after 60 minutes of pushing in women with occiput posterior deliveries were 92.5% (91.2-93.6) and 72.9% (69.5-75.9), respectively, and increased to 97.4 (96.3-98.2) and 82.6 (78.3-86.1) with pushing until 90 minutes, but did not increase beyond these time limits.
Active pushing more than 30 minutes was associated with higher rates of adverse maternal outcomes and with lower Apgar scores in all women, and with higher rates of pH<7.0 in parous women.
Conclusion
The estimated probability of a spontaneous delivery varied with parity, the use of epidural analgesia, and with fetal position. The time limits of the pushing phase should be individualized accordingly.