Prior cone biopsy: prediction of preterm birth by cervical ultrasound.

OBJECTIVE: This study was undertaken to determine the predictive accuracy for preterm birth of transvaginal ultrasound (TVU) of the cervix in women with a prior cone biopsy. STUDY DESIGN: Pregnant patients with a history of cervical cone biopsy by cold knife, loop electrosurgical excision procedure (LEEP), or laser were monitored prospectively with TVU of the cervix between 16 and 24 weeks. The predictive value of TVU was evaluated by using less than 25 mm cervical length as criteria for the definition of a short cervix. The primary outcome was spontaneous preterm birth less than 35 weeks. RESULTS: Of 109 women with prior cone biopsy identified, 55 had LEEP, 45 cold knife, and 9 laser cone biopsies. Thirty (28%) had a short cervix, with 9 (30%) having spontaneous preterm birth less than 35 weeks. Seventy-nine (72%) did not have a short cervix, with 5 (6%) having spontaneous preterm birth less than 35 weeks. The sensitivity, specificity, and positive and negative predictive values for spontaneous preterm birth were 64%, 78%, 30%, and 94%, respectively (relative risk [RR] 4.7, 95% CI 1.6-15.3).