Cervical length evolution in pregnancy and prediction of preterm delivery

To construct reference charts for cervical length (CL) in pregnancy based on longitudinal measurements and to assess the value of measuring cervical length after 24 weeks of gestation.

CL was measured transvaginally in singleton pregnancies at 5 to 41 weeks. Pregnancies with more than one measurement were used for creating the CL chart, whereas any measurement after 24 weeks was considered for assessing the correlation of CL with preterm delivery.

The dataset consisted of 12,601 pregnancies and 33,899 observations. Gestational age was the main predictor of CL (R² = 67.3%). Further adjustments in the fixed effects part for maternal characteristics (age, BMI, smoking status, parity, history of miscarriage, and cervical surgery) improved the prediction ability (R² = 78.4%). CL was predictive of spontaneous preterm delivery before 37 weeks when measured at any gestation between 24 and 35 weeks and it was predictive of spontaneous preterm delivery before 32 weeks when measured between 28 and 31 weeks (AUC = 0.68).

Gestational age is the main predictor of CL followed by maternal characteristics and history. CL assessment between 24 and 35 + 6 weeks can enhance our ability to predict spontaneous preterm delivery.