BACKGROUND
Late preterm neonates born between 34.0 and 36.6 weeks’ gestation are at increased
risk for short- and long-term morbidity and mortality when compared with their term
counterparts. Currently, no separate labor curve is available for late preterm births,
and this group's optimal duration of the second stage of labor has never been defined
separately.
OBJECTIVE
This study aimed to compare the second stage duration between late preterm and term
births.
STUDY DESIGN
This was a retrospective study from May 2014 until May 2021. Eligible were women with
a singleton pregnancy, vertex presentation, spontaneous or induced onset of labor,
and those who delivered vaginally beyond 34.0 weeks of gestation. The primary outcome
of our study was to compare and characterize the second stage of labor duration between
late preterm and term births.
RESULTS
We analyzed 962 late preterm and 9476 term vaginal deliveries. Women who delivered
during the late preterm period were more likely to be multiparous (52.4% vs 45.2%;
P<.001) and fewer required oxytocin during labor (41.2% vs 54.4%; P<.001) or used epidural analgesia (75.2% vs 83.6%; P<.001). The overall mean duration of the second stage of labor was significantly shorter
in the late preterm period than at term (1.08±1.09 hours vs 1.49±1.22 hours; P<.001). This was even more pronounced for nulliparous women (1.05±1.00 hours vs 2.10±1.17
hours; P<.001). Among multiparous women, epidural use significantly affected the duration
of the second stage of labor, and the second stage was relatively longer during the
late preterm period than at term in this subgroup (1.16 vs 0.5 hours; P<.001). Using a multivariate Cox regression, variables such as maternal age (hazard
ratio, 1.02; 95% confidence interval, 1.01–1.04), parity (hazard ratio, 4.11; 95%
confidence interval, 3.65–4.63), preterm birth (hazard ratio, 2.08; 95% confidence
interval, 1.4–3.10), and birthweight at delivery (hazard ratio, 1.15; 95% confidence
interval, 1.01–1.30) shortened the second stage, whereas induction of labor (hazard
ratio, 0.75; 95% confidence interval, 0.66–0.86) and epidural use (hazard ratio, 0.68;
95% confidence interval, 0.64–0.86) extended its total duration. Regardless of parity,
lower rates of operative vaginal deliveries were observed in the late preterm period
than at term (3.7% vs 15.5%; P<.001). This period was also associated with lower rates of third- and fourth-degree
perineal lacerations (0.2% vs 2.2%; P<.001) but higher rates of chorioamnionitis (1.7% vs 0.1%; P<.001), Apgar score at 5 minutes <7 (1.0% vs 0.2%; P<.001), and admission to the neonatal intensive care unit (19.3% vs 1.0%; P<.001).
CONCLUSION
Women who delivered vaginally during the late preterm period had a distinctive second-stage
duration. Primarily, it was shown to be significantly shorter for nulliparous and
multiparous women. Future studies should further clarify the optimal duration of this
stage in relation to neonatal outcomes at such a vulnerable period.
Key words
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Article info
Publication history
Published online: December 23, 2022
Accepted:
December 20,
2022
Received in revised form:
December 6,
2022
Received:
September 16,
2022
Footnotes
O.G. and N.J. contributed equally to this work.
The authors report no conflict of interest.
This study did not receive any funding.
This study was presented at the 42nd annual meeting of the Society for Maternal-Fetal Medicine, held virtually, January 31–February 5, 2022.
Cite this article as: Gutzeit O, Justman N, Ben Zvi Z, et al. Late preterm delivery has a distinctive second-stage duration and characteristics. Am J Obstet Gynecol MFM 2022;XX:x.ex–x.ex.
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