Gestational age reference from crown-rump length during 11-14 weeks: a population-based multicenter cohort study in China.

Abstract

Background: This study aimed to develop a new ultrasonographic dating formula to estimate gestational age (GA) based on fetal crown-rump length (CRL) in a Chinese population, evaluate model accuracy and compare its performance with established dating formulas.

Methods: A prospective, multicenter study was conducted across mainland China. Participants included healthy, low-risk women with spontaneously conceived singleton pregnancies and a regular menstrual cycle in the preceding year. Ultrasonography was performed between 11 and 14 weeks of gestation, with GA determined based on the last menstrual period. Participants were randomly assigned to a development or validation cohort in a 7:3 ratio. A best-fit regression model was constructed for GA estimation based on CRL in the development cohort. For validation, mean differences between the new estimated GA and menstrual age were calculated and compared with those obtained using five established CRL-based dating formulas in the validation cohort. All participants were followed through to delivery.

Results: The study recruited 4,710 women with singleton pregnancies, with 3,297 in the development cohort and 1,413 women in the validation cohort. The mean and standard deviation values of CRL changed linearly with GA during 11-14 weeks. CRL demonstrated a linear relationship with GA between 11 and 14 weeks, yielding the regression equation GA = 59.590085 + 0.458539×CRL (R² = 0.8042). The mean difference between estimated GA and menstrual age was 0.32 days (95% confidence interval 0.17-0.46), demonstrating a smaller error compared with those obtained from the five widely used CRL dating formulas.

Conclusions: We derived a CRL-based dating formula applicable to naturally conceived pregnancies at 11-14 weeks. This new formula exhibits small residuals, providing a more accurate alternative to existing CRL-based dating formulas.