Choosing the Equation for Estimated Gestational Age With Crown-Rump Length

Abstract

Background: The aim of our study was to approach the equation most robust for gestational age (GA) estimation in our clinical setting. Six recent equations are assessed. Methods: A total of 484 single normal pregnancies, from the trisomy screening program at Consorci Hospital General Universitari of Valencia, Spain were assessed for differences in GA estimations, with duplicated crown-rump length (CRL) measurements taken at least 1 week apart. Regression and Chi-square test was applied for comparing results, considering significant if P < 0.05. Results: The differences in GAs using the same CRL were as high as 11 days at 90 mm, but at 20 to 65 mm are only 1 - 2 days. The GA estimation has low reproducibility when based on two CRL measurements, but one equation achieved a GA difference of ± 5 days in 97.1% of cases, which is significantly higher than any other equation. Five equations are influenced by the interval between the CRL measurements. Conclusions: The differences between GA estimations based on successive CRL measurements could be clinically significant. Understanding the equation's behavior is essential to choose the optimal equation for a specific clinical setting. We identified an equation with higher reproducibility. J Clin Gynecol Obstet. 2021;10(2):46-50 doi: https://doi.org/10.14740/jcgo738