Additional risk stratification in women with a history of spontaneous preterm birth and a midtrimester cervical length > 25 millimeters

Purpose: To determine whether there is an association between cervical length > 25 millimeters (mm) and a decrease in cervical length before 24 weeks of gestation with an increased risk of recurrent spontaneous preterm birth (sPTB).” Methods: This retrospective cohort study includes women with a singleton pregnancy, a previous sPTB before 34 weeks of gestation, serial cervical length measurements and a shortest midpregnancy cervical length of > 25 mm. Participants received care according to local protocols for the prevention of preterm birth in two academic hospitals in the Netherlands between February 2005 and September 2021. Exclusion criteria were fetal structural anomalies, signs of threatened preterm birth or treatment with a cerclage or pessary. Cervical length measurements were grouped in three timepoints in pregnancy that were chosen a priori: 14 + 0 to 18 + 6 weeks (CL1); 19 + 0 to 20 + 6 weeks (CL2); and 21 + 0 to 23 + 6 weeks (CL3). Outcome measures included percentage of sPTB (< 37, < 34 and < 28 weeks of gestation) with 95% confidence intervals (95% CI) and Odds Ratio’s (OR). Association between decrease in cervical length and sPTB were calculated using logistic regression. Results: In total, 469 pregnancies were included. Overall, sPTB recurred in 21.1% (95% CI 17.4–24.8%), 9.0% (95% CI 6.4–11.6%) and 1.9% (95% CI 0.7–3.2%) before 37, 34 and 28 weeks of gestation, respectively. Women with a cervical length of > 25–30 mm in CL3 were at higher risk to deliver before 37 weeks, compared to women with a cervical length > 30 mm (44.7% versus 18.5%, OR 3.6, 95% CI 1.91–6.66). The decrease in cervical length between timepoint CL1, CL2 and CL3 had no association with a recurrent sPTB. Conclusions: Women with a history of sPTB before 34 weeks of GA and a cervical length of > 25–30 mm before the 24 weeks of gestation have an almost four times higher risk for a recurrent sPTB, compared to those with a longer cervical length. No association was found between decrease in cervical length and the risk of sPTB. Future studies should assess whether women with a history of sPTB and a cervical length of > 25–30 mm benefit from cerclage and cutoff values could be revised accordingly.