 Women with a prior early spontaneous preterm birth and a shortened mid-trimester cervical length less than 25 mm are at very high risk for having another premature baby. The Vaginal Ultrasound Cerclage Trial is a multicenter, randomized clinical trial designed to determine the efficacy of cerclage a purse-string suture placed around the uterine cervix for the prevention of spontaneous preterm birth prior to 35 weeks gestation. The study will evaluate women at significant risk for recurrent spontaneous preterm birth those with a prior spontaneous birth at 17 to 32 weeks gestation and who have an increased risk based on mid-trimester ultrasound findings of a cervical length less than 25 mm. 