McDonald versus Shirodkar cervical cerclage for the prevention of preterm birth: impact of body mass index.

Objective: To compare obstetrical outcomes on women undergoing a McDonald or Shirodkar cerclage and to estimate the impact of maternal body mass index (BMI) on these outcomes. Methods: We conducted a retrospective review of the medical records of all women with singleton pregnancies who underwent placement of a McDonald or Shirodkar cerclage at St. Francis Hospital from January 2008 to October 2013. The subjects were categorized based on BMI groups (normal: less than 25 kg/m2, overweight: 25-29 kg/m2, obese: 30 kg/m2 or more). The primary outcome was gestational age at delivery. Statistical analyses included chi-square, Student's t-test, and multivariable regression analysis. Results: Of 95 women, 47 (49.5%) received a Shirodkar, and 48 (50.5%) a McDonald cerclage. 16 women (16.8%) were categorized as normal weight, 35 (36.8%) as overweight, and 44 (46.3%) as obese. Gestational age at delivery differed significantly by group, decreasing with each categorical increase in BMI (normal: 39.0 ± 0.3 weeks; overweight: 36.6 ± 0.7 weeks; obese: 33.0 ± 1.1 weeks; p < .01). Overall, women receiving a Shirodkar cerclage had significantly longer pregnancies than women with a McDonald cerclage (36.7 ± 0.6 weeks versus 33.9 ± 1.0 weeks; p = .02). However, analysis showed a significant interaction between weight status and gestational age at delivery. Obese women had significantly longer pregnancies when they received a Shirodkar cerclage versus a McDonald cerclage (32.6 ± 1.0 weeks versus 28.8 ± 0.9 weeks; p < .01). However, there was no significant difference in gestational age at delivery between women categorized as normal/overweight (Shirodkar: 33.5 ± 0.9 weeks; McDonald: 32.9 ± 0.9 weeks; p = .63). Conclusions: Compared to obese women receiving a McDonald cerclage, obese women receiving a Shirodkar cerclage had significantly longer pregnancies. No significant differences in pregnancy duration were found in normal/overweight women regardless of cerclage technique. Pregnancy duration in obese women receiving a Shirodkar cerclage was similar to the pregnancy duration of normal/overweight women.