(1) Background: We aimed to investigate whether second-stage cesarean delivery (SSCD) had a higher occurrence of low-segment uterine incision extensions compared with cesarean delivery (CD) at other stages of labor and to study the association of these extensions with preterm birth (PTB). (2) Methods: In this retrospective longitudinal follow-up cohort study, spanning from 2006 to 2019, all selected mothers who delivered by CD at first birth (P1) and returned for second birth (P2) were grouped by cesarean stage at P1: planned CD, first-stage CD, or SSCD. Mothers with a PTB at P1, multiple-gestation pregnancies in either P1 or P2 and those with prior abortions were excluded. (3) Results: The study included 1574 selected women who underwent a planned CD at P1 (n = 483 (30.7%)), first-stage CD (n = 878 (55.8%), and SSCD (n = 213 (13.5%)). There was a higher occurrence of low-segment uterine incision extensions among SSCD patients compared to first-stage CDs and planned CDs: 50/213 (23%), 56/878 (6.4%), and 5/483 (1%), respectively (p < 0.001). A multivariate logistic regression showed that women undergoing an SSCD are at risk for low-segment uterine incision extensions compared with women undergoing a planned CD, OR 28.8 (CI 11.2; 74.4). We observed no association between the occurrence of a low-segment uterine incisional extension at P1 and PTB ≤ 37 gestational weeks in the subsequent delivery, with rates of 6.3% (7/111) for those with an extension compared to 4.5% (67/1463) for those without an extension (p = 0.41). Notably, parturients experiencing a low-segment uterine incisional extension during their first childbirth were six times more likely to have a preterm delivery before 32 weeks of gestation compared to those without extensions, with two cases (1.8%) compared to four cases (0.3%), respectively. A similar trend was observed for preterm deliveries between 32 and 34 weeks of gestation, with those having extensions showing twice the prevalence of prematurity compared to those without, with a p-value of 0.047. (4) Conclusions: This study highlights that mothers undergoing SSCD experience higher prevalence of low uterine incision extensions compared to other CDs. To further ascertain whether the presence of these extensions is associated with preterm birth (PTB) in subsequent births, particularly early PTB before 34 weeks of gestation, larger-scale future studies are warranted.
Keywords: lower uterine incision extensions; preterm birth; second-stage cesarean delivery.