Predicting preterm birth in women with previous preterm birth and cervical length ≥ 25 mm

To identify risk factors predicting subsequent spontaneous preterm birth or preterm prelabor rupture of membranes (PPROM) in a cohort of women with a history of spontaneous preterm birth and a cervical length of ≥ 25 mm at 20-24 weeks' gestation.

We identified all pregnant women who attended our preterm labor clinic between January 2010 and December 2012 because of previous spontaneous preterm birth or PPROM before 34 weeks. Women with a normal cervical length (defined as ≥ 25 mm) between 20 and 24 weeks' gestation were identified and included in the analysis. Maternal characteristics, obstetric history, shortest cervical length and gestational age at shortest cervical length of women who delivered preterm (before 37 weeks) were compared with those who delivered at or after 37 weeks in the index pregnancy. Multiple regression analysis was planned to examine the relationship between significant clinical and cervical-length variables to identify significant clinical predictors of spontaneous preterm birth among high-risk patients with a normal cervix between 20 and 24 weeks' gestation.

Of 134 women with a normal cervix at 20-24 weeks, 28 (20.9%) delivered spontaneously or had PPROM before 37 weeks; of these 12 (9.0%) delivered before 34 weeks. None of the selected explanatory variables was predictive of recurrent preterm birth in this cohort. No correlation between absolute cervical length and gestational age at delivery was found (R = 0.01).

In high-risk women with a cervical length of ≥ 25 mm at 20-24 weeks' gestation, demographic characteristics and absolute cervical length are not useful in predicting subsequent spontaneous preterm birth.