Objective: To determine which factors increase the risk of large caesarean scar defects as assessed by transvaginal ultrasound.
Design: Observational cross-sectional study.
Setting: University Hospital.
Population: One hundred and eight women who had undergone one caesarean section.
Methods: Transvaginal ultrasound examination of the scar in the uterus 6-9 months after the caesarean. Published ultrasound definitions of large scar defects were used. Clinical information was obtained from medical records after all ultrasound images had been evaluated.
Main outcome measures: Factors increasing the risk of large caesarean scar defects.
Results: Twenty-two (20%) women had a large caesarean scar defect. The odds of a large defect increased with cervical dilatation at caesarean (0 cm, 1-4 cm, 5-7 cm, 8 cm or more; odds ratio [OR] 4.4 [95% CI 0.7-28.5]; 26.5 [4.3-161.8]; and 32.4 [6.1-171.0]; P < 0.001), station of the presenting part at caesarean below pelvic inlet (OR 14.1 [4.6-43.1]; P < 0.001), duration of labour at caesarean (0 hour, 1-4 hours, 5-9 hours, 10 hours or more; OR 2.0 [0.2-23.8]; 13.0 [2.2-76.6]; and 33.1 [6.6-166.9]; P < 0.001), oxytocin augmentation (OR 6.3, [2.3-17.3]; P < 0.001), retroflexed uterus at ultrasound examination (OR 2.9 [1.0-8.3]; P = 0.047). According to multivariate logistic regression, no variable added information to cervical dilatation or the station of the presenting fetal part at caesarean.
Conclusions: Caesarean in advanced labour is associated with increased risk of incomplete healing of the uterine incision as determined by transvaginal ultrasound.