Second trimester cervical length and prolonged pregnancy (.).

Objective: To determine whether second trimester transvaginal ultrasound cervical length (CL) is associated with prolonged pregnancy (≥41 0/7 weeks) in nulliparous women who reach term (≥37 weeks) with a planned vaginal delivery.

Methods: Retrospective cohort of nulliparous singletons 18 0/7-23 6/7 weeks gestation undergoing CL screening from 1/1/12 to 12/31/13. Women who delivered at term with spontaneous labor or reached 41 weeks were included. Primary outcome was incidence of prolonged pregnancy. Risk of prolonged pregnancy was assessed by CL quartile using odds ratio, adjusted for confounders (aOR) and a receiver operating characteristic (ROC) curve.

Results: 722 women were included, among them 171 (24%) had a prolonged pregnancy. There was a significant difference in BMI and race across CL quartiles. The aOR of having a prolonged pregnancy with CL in quartiles 2, 3, and 4 versus quartile 1 were 2.14(1.27-3.62), 2.72(1.59-4.65), and 1.69(1.02-3.03), respectively. CL ≥ 37 mm (beyond first quartile) was associated with a two-fold increased risk of prolonged pregnancy versus CL < 37 mm, (27% vs 15%, p < 0.01, aOR 2.17 (1.38-3.41)). ROC curve did not identify a CL cutoff that was predictive of prolonged pregnancy (AUC 0.544, p = 0.079).

Conclusions: Although a longer second trimester CL is associated with an increased risk for prolonged pregnancy, it is not predictive.