Cerclage for Twins With Short Cervix

Inclusion Criteria: * Twin pregnancy (see Exclusion Criterion (a) below re: monochorionic twins) * Gestational age 16 0/7 to 25 6/7 weeks at time of enrollment by best-estimated age. * Cervical length 0.1 to 15.0 mm on transvaginal ultrasound examination. (Cervical length is taken to mean the length of the closed portion of the cervical canal. Exclusion Criteria: * Maternal age less than 18 years * Monochorionic twins (such as monochorionic-diamniotic, monochorionic-monoamniotic, or conjoined twins) * Rupture of membranes, either twin * One or both twins has no cardiac activity * One or both twins has known or suspected major malformation, aneuploidy, or polyhydramnios * Maternal congenital uterine anomaly (such as bicornuate uterus, unicornuate uterus) * Pregnancy started as triplets or higher-order multifetal gestation and then reduced to twins, either spontaneously or via procedure * Symptomatic uterine contractions, 6 or more per hour * Ongoing bleeding from uterus * Patient declines to consider cerclage * Patient declines treatment with vaginal progesterone * Allergy to progesterone or peanuts (because the vaginal progesterone formulation used will be a capsule of micronized progesterone in peanut oil.) * Cerclage is already in place * Cerclage placement is judged to be technically impossible * Patient has a history of poor follow-up or poor adherence to physician recommendations * Patient is planning to relocate outside the local area before the end of pregnancy such…