Mid-pregnancy cervical length and pregnancy outcomes in nulliparous and low-risk multiparous singleton pregnancies: A prospective cohort study (the Quadruple P Screening Study).

OBJECTIVES

This study evaluated the association between midtrimester cervical length (CL) and pregnancy outcomes in low-risk nulliparous and multiparous singletons and assessed whether combining CL with obstetric and medical history improved the prediction of spontaneous preterm birth (sPTB).

STUDY

DESIGN

This multicenter prospective cohort study included singletons without prior sPTB < 34 weeks who had CL measured at 18-22 weeks GA. Outcomes were retrieved through linkage with the national perinatal registry. Primary outcome was sPTB < 37 weeks. Secondary outcomes included PTB rates, NICU admission and perinatal death. Sensitivity and specificity were calculated per CL group. GA at birth was analyzed using Kaplan-Meier curves, and predictors were assessed using multivariable Cox regression with hazard ratios (HR) and 95% confidence intervals (CI). Results are reported separately for nulliparous and multiparous singletons.

RESULTS

We retrieved 15,524 pregnancy outcomes following a CL measurement between 2015-2022. In nulliparous singletons (N = 8,078), sPTB < 37 weeks occurred in 31.0%, 8.7%, 9.3%, and 3.5% for CL ≤ 25, 26-30, 31-35, and > 35 mm, respectively. CL ≤ 25 mm identified 7.8% of sPTB < 37 weeks and 31.3% of sPTB < 32 weeks. In multiparous singletons (N = 7,446), rates were 17.2%, 7.9%, 5.2%, and 2.3%, with CL ≤ 25 mm identifying 5.6% of sPTB < 37 weeks and 24.2% of sPTB < 32 weeks. Multivariable Cox regression showed that in nulliparous singletons, only CL categories were associated with sPTB < 37 weeks compared with the reference > 35 mm, with the highest hazard for CL ≤ 25 mm (HR 10.8, 95% CI 6.3-18.8; p < 0.0001). In multiparous singletons, CL ≤ 25, 26-30, and 31-35 mm (p < 0.0001, p = 0.001, p = 0.04), low SES (p = 0.03), smoking (p < 0.0001), and an interpregnancy interval < 6 months (p = 0.02) were significantly associated.

CONCLUSION

This study confirmed the strong inverse correlation between midtrimester CL and sPTB risk, with multivariable regression analyses reinforcing CL as the dominant predictor. Given its ability in identifying those at highest risk, particularly for sPTB < 32 weeks, universal CL measurements should be central to PTB prevention strategies.