Vaginal ultrasound and cervical cerclage: a prospective study.

Vaginal ultrasound is a new technique for the objective assessment of the pregnant cervix. Twenty patients (21 pregnancies) were scanned at regular intervals throughout pregnancy after cervical cerclage by the vaginal route. Patients were recruited in 2 consecutive years in each of two centers with a low incidence of cervical cerclage (less than 0.5% of all pregnancies). Cervical cerclage, using Mersilene tape inserted by anterior and posterior incisions, positioned the cervical suture in the middle third of the cervical canal in all procedures (21/21). Ultrasound features including dilatation of the internal cervical os and herniation of the gestational sac to the level of the cervical suture were detected in 4/21 pregnancies at 5-7 weeks prior to delivery (21-33 weeks). Six patients (6/21) delivered preterm (< 37 weeks) without ultrasound features associated with cervical incompetence. Eleven patients (11/21) had a closed internal cervical os throughout pregnancy that remained closed after removal of the cervical suture at 38 weeks. In this study ultrasound features associated with cervical incompetence had a sensitivity of 40% and a specificity of 100% in the prediction of preterm pregnancy loss in this group of patients undergoing cerclage. Vaginal ultrasound is a simple, non-invasive technique that permits the detection of ultrasound features associated with cervical incompetence during pregnancy in patients who have had prophylactic cervical cerclage at 14-16 weeks' gestation. Ultrasound features associated with cervical incompetence were rare in this group of patients (4/21 from an overall obstetric population of 8000 deliveries) indicating a prevalence of cervical incompetence in the range of 1 : 1000-1 : 2000 deliveries. In the majority of patients undergoing cerclage (11/21) the clinical diagnosis of 'cervical incompetence' was incorrect as shown by the detection of a normal cervical canal following removal of the suture at 38 weeks.