EP08.13: Evaluation of fetal growth charts: a comparative study in a local population

To evaluate the impact of applying different fetal growth charts for estimated fetal weight (EFW) at the second and third trimester, in our local population, and to compare their ability to predict small or large for gestational age (SGA or LGA) fetuses. In this retrospective observational study, we reviewed all pregnant women (n = 7059) who had an ultrasound assessment at Axa Medical private prenatal centre. We included live, singleton pregnancies, with biometry performed between 20 to 41 gestational weeks. Gestational age was confirmed by first trimester ultrasound, and EFW was calculated using Hadlock3 formula. We calculated the Z-scores using four reference curves, Hadlock4 (1985), INTERGROWTH-21 (2012), World Health Organization (WHO) (2017) and Fetal Medicine Foundation (FMF) (2018). The Z-score was compared with the expected normal distribution by calculation of the mean and SD. We calculated the proportions of fetuses <3rd and <10th percentiles, and >90th and >97th percentiles for EFW, using these charts. Finally, 13517 EFW evaluations were available. Based on the analysis of the Z-score distribution, the best fit for our population was the FMF reference curve (mean -0.01, SD 1.51), followed by INTERGROWTH-21 (mean 0.236, SD 1.2), Hadlock4 (mean -0.261, SD 0.92) and WHO (mean -0.297, SD 0.98) curves. The proportion of small fetuses (<3rd centile) was 8.01%, 3.01%, 4.01% and 2.6%, respectively for FMF, INTERGROWTH-21, Hadlock4 and WHO reference curves. The same charts classified respectively 10.3%, 7.2%, 9.7% and 7.1% of fetuses <10th percentiles. Similarly, the proportion of large fetuses (>90th percentile) was respectively 16.6%, 16.5%, 2% and 17.8% for these curves. In our population, the best match was achieved by the FMF curve. However, this chart recognised many fetuses as <3rd percentile, which may involve additional monitoring. FMF, Intergrowth-21 and WHO yielded high proportions of >90th and >97th percentiles. The number of fetuses characterised as SGA or LGA varies significantly depending on the reference table used.