Impact of cervical length on preterm birth in northern China: a prospective cohort study.

Aim: To evaluate the association between cervical length (CL) and certain subtypes of preterm birth (PTB).Materials and methods: Data were derived from a prospective cohort study conducted in China to explore the risk factors of PTB between 2012 and 2014. Gestational age was based on transvaginal ultrasound examination during pregnancy. PTB was categorized into two subtypes according to its clinical symptoms. Logistic regression was used to evaluate the relation between short CL and certain subtypes of PTB, adjusted for potential confounders.Results: Of the 3688 women included in the analysis, 425 (11.5%) women had a CL less than 30 mm (short CL). The incidence of PTB was significantly higher in the short CL group than the normal CL group (10.6 versus 6.0%; adjusted risk ratio (RR) 1.91, 95% CI 1.35, 2.69). The association between short CL and overall PTB was both significant in primipara (adjusted RR 2.00, 95% CI 1.09, 3.68) and multipara (adjusted RR 1.89, 95% CI 1.24, 2.87). The association between short CL and noniatrogenic PTB related to parity (primipara adjusted RR 2.13, 95% CI 1.11, 4.10; multipara adjusted RR 1.90, 95% CI 1.21, 3.00).Conclusion: Short CL could increase the risk of overall PTB and noniatrogenic PTB. The association between CL and noniatrogenic PTB was dependent on parity.