Why do nulliparous teenagers have the highest rate of unassisted vaginal deliveries compared to their older counterparts?

Authors

Pierre-Yves Robillard, Silvia Iacobelli, Malik Boukerrou, Brahim Boumahni, Francesco Bonsante, Phuong Lien Tran, Gustaaf Dekker

Published in

The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians. Volume 38. Issue 1. Pages 2503509. Epub Jun 08, 2025.

Abstract

To establish why teenagers (13-19 years old) primiparas have higher rates of unassisted vaginal deliveries compared with their older counterparts.
University's maternity, 24.5-year-observational population-based cohort study (2001-2024). All consecutive nulliparous singleton pregnancies. Analysis of the main indications for cesarean sections (c-sections) and also need for operative vaginal procedures of all nulliparous pregnant women with an age range from 14 to 40+ yrs.
Out of 33,785 singleton primiparous livebirth pregnancies, vaginal births represented 91% at the ages 14-15 dropping to just 55% at ≥40 yrs. The rate of c-sections was 9% at the ages 14-15, increasing to a rate of 45% at ≥40 years. Operative vaginal delivery rate was 12.1% at the ages 14-15 years, versus 29.8% at ≥ t 40 years (both χ² for trend, p < .0001). Two-thirds of the indications for c-sections were "abnormal fetal monitoring" (AFM) and "Obstructed Labor" (OL). The indication AFM had a χ² for a negative linear trend p = .0004: a high rate of 39% for the ages 14-15, and 25% for the ages over 40 years. The indication OL had a positive trend with maternal ages but not linear (p = .13): 17% for the ages 14-15 years, 25% for the ages 16-19, followed by a plateau around 32% between 20 and 40 years.
Vaginal births in primiparas without obstetrical assistance occur preferably at younger ages with a regular negative linear trend, p < .001 until the ages 40+. The indication AFM for c-sections also had a negative linear trend, p = .0004, while OL as indication for c-sections represented a minority in teenagers (below breech presentation). In teenagers, the higher rate of unassisted vaginal births may be due to an intrinsic biologic cause (uterine contractility).

PMID:
40484702
Bibliographic data and abstract were imported from PubMed on 09 Jun 2025.

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