Large uterine leiomyomata and risk of cesarean delivery

OBJECTIVE: To study the causes of the observed association between presence of leiomyomata in pregnancy and increase in risk of cesarean delivery. METHODS: We accessed the obstetric database of women who underwent second-trimester ultrasound screening between January 1996 and December 2004 and who delivered at more than 22 weeks of gestation. Ultrasonographic characteristics of the leiomyomata, including number, maximum diameter, change in size during pregnancy, and location were recorded. Pregnancy outcome was compared between the cohort with large uterine leiomyomata (5 cm or more) (n=251) and those without leiomyomata (n=24,546) using chi(2), Fisher exact test, Student t test, and linear and logistic regression analysis, with an odds ratio (OR) with 95% confidence interval (CI) not inclusive of the unity considered significant. RESULTS: Women with large leiomyomata had higher rates of cesarean delivery before onset of labor (OR 3.1, 95% CI 2.2-4.2) but not during labor (OR 1.0, 95% CI 0.6-1.6). The association between leiomyomata and cesarean delivery before labor remained significant after controlling for maternal age, nulliparity, fetal mal presentation, and placenta previa (OR 2.1, 95% CI 1.4-3.1). The only ultrasonographic leiomyoma characteristic independently associated with cesarean delivery before labor after controlling for confounders was maximum diameter of the largest leiomyoma (OR 1.3, 95% CI 1.1-1.4, P=.001). CONCLUSION: Uterine leiomyomata 5 cm or larger are independently associated with cesarean delivery performed before labor, and the risk increases with the size of the leiomyoma.