Mid-pregnancy cervical length as a risk factor for cesarean section in women with twin pregnancies

It is well known that a short cervix at mid-pregnancy is a risk factor for spontaneous preterm birth in both singleton and twin gestations. Recent evidence also suggests that a long cervix at mid-pregnancy is a predictor of the risk of cesarean section (C/S) in singleton gestation. The purpose of this study was to determine whether a long cervix at mid-pregnancy was associated with an increased risk of C/S in women with twin pregnancies. We enrolled 746 women pregnant with twins whose cervical length was measured by trans-vaginal ultrasonography at a mean of 22 weeks of gestation and who delivered in our institution. Cases with a short cervix [cervical length (CL) <15 mm] were excluded. Cases were divided into four groups according to the quartile of CL. The rate of C/S increased according to the quartile of CL (47% in the 1 ^st quartile, 51% in the 2 ^nd quartile, 56% in the 3 ^rd quartile and 62% in the 4 ^th quartile, P<0.005, χ ² for trend). CL was an independent risk factor for C/S even after adjustment for confounding variables. When confining analysis to women who delivered after a trial of labor (n=418), to nulliparous women (n=633) or to those who delivered at late preterm or full term (n=666), the rate of C/S also increased according to the quartile of CL, and the relationship between CL and the risk of C/S remained significant after adjustment in each group. In women pregnant with twins, long CL at mid-pregnancy was a risk factor for C/S.