Second trimester cervical length and risk of preterm birth in women with twin gestations treated with 17-α hydroxyprogesterone caproate

Objective. To compare rates of preterm birth before 35 weeks based on cervical length measurement at 1620 weeks in women with twin gestations who received 17-α hydroxyprogesterone caproate (17OHPC) or placebo. Methods.This is a secondary analysis of a randomised, double-blind, placebo-controlled trial of twin gestations exposed to 17OHPC or placebo. Baseline transvaginal ultrasound evaluation of cervical length was performed prior to treatment assignment at 1620 weeks. Cervical length measurements were categorised according to the 10th, 25th, 50th and 75th percentiles in the women studied. The effect of 17OHPC administration in women with a short (25th percentile) and long (75th percentile) cervix was evaluated. Results.Of 661 twin gestations studied, 221 (33.4) women enrolled at 11 centers underwent cervical length measurement. The 10th, 25th, 50th, 75th percentiles for cervical length at 1620 weeks were 32, 36, 40 and 44mm, respectively. The risk of preterm birth<35 weeks was increased in women with a cervical length<25th percentile (55.8 vs. 36.9, p=0.02). However, a cervical length>75th percentile at this gestational age interval was not protective for preterm birth (36.5 vs. 42.9, p=0.42). Administration of 17OHPC did not reduce preterm birth before 35 weeks among those with either a short or a long cervix (64.3 vs. 45.8, p=0.18 and 38.1 vs. 35.5, p=0.85, respectively). Conclusion.Women with twin gestations and a cervical length below the 25th percentile at 1620 weeks had higher rates of preterm birth. In this subgroup of women, 17 OHPC did not prevent preterm birth before 35 weeks gestation. A cervical length above the 75th percentile at 1620 weeks did not significantly reduce the risk of preterm birth in this high risk population.