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

Elena de la Fuente-Diez, Francisco Tomas-Bosch, Jose J. Santonja-Lucas


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


Gestational age estimation; Crown-rump length; Equations for gestational age; Crown-rump growth

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Journal of Clinical Gynecology and Obstetrics, quarterly, ISSN 1927-1271 (print), 1927-128X (online), published by Elmer Press Inc.                     
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