The duration of labor in spontaneous preterm deliveries: A retrospective observational study in a tertiary Irish maternity hospital

Background: Preterm deliveries account for 10% of all births, and are the most important cause of neonatal mortality globally. Despite their frequency, there is a paucity of information known about usual patterns of preterm labor, as previous studies which critically defined the normal progression of labor excluded preterm gestations. Objective: To compare the durations of the first, second and third stages of spontaneous preterm labor in nulliparous and multiparous women at varying preterm gestations.Methods: A retrospective observational study was undertaken of women admitted in spontaneous preterm labor from January 2017 to December 2020 with viable singleton gestations between 24 and 36 + 6 weeks' gestation who then proceeded to have a vaginal delivery. There were 512 cases following exclusion of preterm inductions of labor, instrumental vaginal deliveries, provider-initiated pre-labor Caesarean sections and emergency intra-partum Caesarean sections. The data was then examined to determine our outcomes of interest including the durations of the first, second and third stages of preterm labor, analyzing results by parity and gestation. For comparison, we reviewed data of term spontaneous labors and spontaneous vaginal deliveries during the same study period, identifying 8339 cases.Findings: 97.6% of participants achieved a spontaneous cephalic vaginal delivery with the remainder undergoing an assisted breech birth. 5.7% of gestations delivered spontaneously between 24 + 0 and 27 + 6 weeks, with most births at gestations greater than 34 weeks (74%). The second stage duration (mean 15 vs 32 vs 32 mins respectively) was significantly different across the three gestation periods (p < 0.05), but was notably much quicker in extremely preterm labors. The first and third stage durations were similar between all gestational age groups with no statistically significant differences in results. There was a significant influence of parity on the first and second stages of labor, with multiparous women progressing more quickly than nulliparae (p < 0.001).Conclusion: The duration of spontaneous preterm labor is described. Multiparous women progress more quickly in the first and second stages of preterm labor than nulliparous women.