Follow-up cervical length in asymptomatic high-risk women and the risk of spontaneous preterm birth

Objective: To determine whether further cervical length shortening by transvaginal ultrasonography in asymptomatic high-risk women with a short cervical length adds additional predictive value for spontaneous preterm birth and perinatal morbidity. Study Design: Women with a history of spontaneous preterm birth, loop electrosurgical excision procedure, cone biopsy or uterine anomaly, who were pregnant with singleton gestations and were found by transvaginal ultrasonography to have a cervical length < 3.0 cm at 20 to 28 weeks' gestation, and who underwent a follow-up cervical length within 3 weeks were evaluated, comparing those with further cervical length shortening (> 10%) to those without further shortening. Primary outcomes were spontaneous preterm birth < 35 weeks' gestation and perinatal morbidity. Secondary outcomes included spontaneous preterm birth < 37 weeks, < 34 weeks, < 32 weeks, birth weight < 2500 g, maternal and other neonatal outcomes. Result: Compared with women without further cervical shortening, those with further shortening were found by univariate analyses to have higher rates of spontaneous preterm birth < 35 weeks (34.8 versus 8.5%, P = 0.014), < 37 weeks (56.5 versus 21.3%, P = 0.003), < 34 weeks (30.4 versus 2.1%, P = 0.001), < 32 weeks (21.7 versus 0%, P = 0.003), birth weight < 2500 g (60.9 versus 17.0%, P < 0.0001), neonatal intensive care unit admission (47.8 versus 17.0%, P = 0.006) and composite perinatal morbidity (43.5 versus 14.9%, P = 0.009). Logistic regression revealed the only independent predictors of spontaneous preterm birth < 35 weeks were further cervical length shortening (adjusted odds ratio (aOR) 5.73; 95% confidence interval (CI) 1.31 to 24.43) and gestational age at short cervical length (aOR 0.95; 95% CI 0.91 to 0.99). Conclusion: Further cervical length shortening in asymptomatic high-risk women with a short cervical length is an important independent predictor of spontaneous preterm birth < 35 weeks and perinatal morbidity. Journal of Perinatology (2011) 31, 318-323; doi:10.1038/jp.2010.149; published online 23 December 2010