Supplementary Material for: New First-Trimester Crown-Rump Length Equations from a French General Population

Introduction: The purpose of this study was to obtain precise knowledge of fetal biometric measurements, in particular crown-rump length (CRL). Our results have been carefully compared to equations found in the literature. Materials and Methods: Single-operator measurements of 2,123 spontaneous pregnancies from a general French population provided new statistical relationships between fetal age (FA) and CRL. Comparisons were made with measurements obtained from 402 in vitro fertilizations (IVFs) for which FA were known. Heteroskedastic and robust regressions were compared by cross-validation, and prediction errors were studied. All ultrasound measurements were taken during standard follow-ups of pregnancies, without any additional features. Results: From a cleaned subsample of 513 spontaneous pregnancies, we reported good modeling of first-term embryonic growth, with equations and predictions of standard deviations agreeing with objective datations for IVFs. Most precise CRL measurements were predicted for FA of 49 days. Discussion: Our results allow future detection of fetal growth abnormalities using Z-scores throughout the first trimester.