Risk Factors for Incomplete Healing of the Uterine Incision After Caesarean Section

Large defects in the uterine scar occur in a significant proportion of women who have undergone cesarean section; the rate of large scar defects increases with the number of cesarean deliveries. It is unknown whether large scar defects are associated with a higher risk of uterine rupture, placenta accreta, and other complications in subsequent pregnancies compared to intact scars or scars with small defects. This observational cross-sectional study, conducted between 2005 and 2006 at a university hospital, investigated factors that increase the risk of large defects in caesarean scars. The study subjects were 108 women who had undergone only 1 cesarean section. Cesarean scar defects were detected and examined by transvaginal ultrasound examinations performed 6 to 9 months after the cesarean. A large scar defect was defined by the most common sonographic parameters described in the medical literature. Clinical information on the current pregnancy and delivery was obtained from medical records after evaluation of all the ultrasound examinations. The primary study outcome measures were factors predictive of large cesarean scar defects. Univariate and multivariate logistic regression were used for statistical analysis. Of the 108 women examined, 22 (20%) women had a large cesarean scar defect. Univariate analysis showed that the risk of a large defect increased with the following factors (expressed as odds ratios and 95% confidence intervals): cervical dilatation at cesarean (1-4 cm: OR 4.4 [95% CI 0.7-28.5]; 5-7 cm: OR 26.5 [4.3-161.8]; 8 cm or more: OR 32.4 [6.1-171.0]; P < 0.001); station of the presenting part below the pelvic inlet (OR 14.1 [4.6-43.1]; P < 0.001), duration of labor (1-4 hours: OR 2.0 [0.2-23.8]; 5-9 hours: OR 13.0 [2.2-76.6]; 10 hours or more: OR 33.1 [6.6-166.9]; P < 0.001), oxytocin augmentation (OR 6.3 [2.3-17.3]; P < 0.001), or retroflexed uterus (OR 2.9 [1.0-8.3]; P = 0.047). Multivariate analysis showed that no variable associated with the cesarean itself, such as 1-versus 2-layer closure, intraoperative complications, or blood loss, added to the risk resulting from cervical dilatation or the station of the presenting fetal part at the time of delivery. These findings indicate that cesarean section in advanced labor increases the risk of incomplete healing of the uterine incision.