Transvaginal ultrasonography in the prediction of preterm birth after treatment for cervical intraepithelial neoplasia

OBJECTIVE: To estimate whether cervical length measured by transvaginal ultrasonography in women having had loop electrosurgical excision procedure (LEEP), cold knife conization, or cryotherapy predicts spontaneous preterm birth. METHODS: Women with a history of LEEP, cold knife conization, or cryotherapy and who were subsequently pregnant with singleton gestations were prospectively compared with both a low-risk control group and women with previous spontaneous preterm birth. A transvaginal ultrasonogram measuring cervical length was performed at 24 to 30 weeks of gestation. Primary outcomes included cervical length and spontaneous preterm birth less than 37 weeks. Secondary outcomes were spontaneous preterm birth less than 34 weeks, low birth weight, and maternal and neonatal outcomes. RESULTS: Women with previous LEEP (N = 75), cold knife conization (N = 21), and cryotherapy (N = 36) had shorter cervical lengths (3.54, 3.69, and 3.75 cm respectively) than the low-risk control group (N = 81, 4.21 cm) (P < .001, P = .03, P = .02 respectively) and similar lengths to women with a previous spontaneous preterm birth (N = 63, 3.78 cm). Loop electrosurgical excision procedure and cold knife conization, but not cryotherapy, were associated with spontaneous preterm birth less than 37 weeks (odds ratio 3.45, 95% confidence interval 1.28-10.00, P = .02; and odds ratio 2.63, 95% confidence interval 1.28-5.56, P = .009, respectively). Using a cutoff of 3.0 cm, transvaginal ultrasonography had a positive predictive value of 53.8% and negative predictive value of 95.2% for spontaneous preterm birth less than 37 weeks in women with LEEP. CONCLUSION: Women with a history of LEEP, cold knife conization, and cryotherapy all independently have shorter cervical lengths than low-risk controls and similar lengths to women with previous spontaneous preterm birth. Loop electrosurgical excision procedure and cold knife conization are associated with spontaneous preterm birth less than 37 weeks, and transvaginal ultrasonography predicts preterm birth in women who have had LEEP.