Risk of preterm birth and second-trimester loss following intrapartum cesarean sections and uterine extensions: a...

Preterm birth (PTB) is associated with significant neonatal morbidity and mortality. Antenatal risk assessment is crucial for prevention and management. Recent evidence suggests that cervical injury during cesarean is a potential risk factor. This study aimed to evaluate the impact of intrapartum cesarean, specifically at full cervical dilatation (CSFD), on subsequent second-trimester loss and preterm birth.

Women delivering by their first term cesarean in 2017 were included in this retrospective cohort study, and data on all subsequent pregnancies till 2024 were extracted. They were divided based on the type of cesarean- elective (CS-E) versus cesarean in latent labour (CS-L), cesarean in active labour (CS-A) and CSFD (± uterine extensions). Adjusted risk ratios (aRR) with 95% confidence intervals (CIs) were calculated to evaluate associations with subsequent pregnancy outcomes.

Among 984 women, 267 had CS-E, 256 had CS-L, 212 had CS-A and 249 had CSFD. The incidence of spontaneous PTB < 37 weeks was 17.9% in CSFD (3-6% in others; p < 0.001). 26.7% of those who had a cesarean for failed instrumental delivery (FID) had a subsequent sPTB. 10.7% (vs. < 1%) and 12.5% (vs. < 6%) of CSFD with 3-5 cm extension had a second-trimester miscarriage and sPTB < 34 weeks, respectively. CSFD group had a 6.5 times higher risk of sPTB < 37 weeks compared to CS-E (CI 2.47-16.9; p < 0.001); the risk increased to 8.2 times in CSFD with 3-5 cm extensions (CI 2.27-29.5, p = 0.001). For every cm increase in cervical dilatation at the time of the index cesarean, the risk increased by 27% (CI 1.14-1.41;p < 0.001). Cesarean for no descent of head and FID had 5.3 times (CI 2.20-12.8; p < 0.001) and 8.7 times higher risk (CI 2.72-28.0; p < 0.001), respectively.

CSFD is associated with a 6.5-fold increase in risk of spontaneous preterm birth. Uterine extension was an important predictor for second-trimester loss and sPTB. Risk assessment for sPTB should potentially include detailed cesarean history, and women with CSFD should potentially be referred to dedicated PTB clinics and offered preventive measures such as serial cervical length assessments, vaginal progesterone and cervical cerclage.