Implementing the INTERGROWTH-21st fetal growth standards in France: a 'flash study' of the College Français d'Echographie Foetale (CFEF)

Abstract

Objectives: To assess potential differences in fetal size between the French population and the international population from the INTERGROWTH-21^st (IG-21^st ) Project and to measure the impact of switching to the IG-21^st reference standards for fetal size.

Methods: This was a nationwide cross-sectional study of fetal ultrasound biometry. Low-risk singleton pregnancies were recruited prospectively within the network of the national French College of Fetal Ultrasound, CFEF, over a 6-week period. Further selection was performed based on the criteria of the IG-21^st Project in order to obtain a comparable population. Head circumference (HC) was used as the main fat-free skeletal measure of growth for comparison of French fetal size with that of the IG-21^st population. The impact of switching to the IG-21^st fetal growth standards was quantified by comparing Z-scores calculated using the IG-21^st standards with those calculated using locally derived reference ranges for HC, abdominal circumference (AC) and femur length (FL).

Results: Following selection, 4858 cases were analyzed. The distribution of HC demonstrated clear similarity between our French population and the IG-21^st population: our observed centile curves closely matched those of IG-21^st and the Z-scores were close to 0 across gestational age. The IG-21^st standards performed as well as did locally derived charts in terms of screening for small-for-gestational age by AC, while they identified significantly fewer small FL values than were expected and than did the locally derived charts.

Conclusions: Under strict selection criteria, fetal size in France is similar to that of the international population used in the IG-21^st Project. The discrepancies in FL are unlikely to impact on prenatal management. Therefore, switching from locally derived reference ranges to the IG-21^st standards appears to be a safe option. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Keywords: biometry; congenital abnormalities; cross-sectional studies; epidemiology; fetal development; growth charts; pregnancy; ultrasound.