Development of Italian Fetal Growth Charts

There is an ongoing international discussion regarding which fetal growth charts should be used. As a matter of fact, an extensive and clinically significant variability among different growth charts has been proved, even between studies of the highest methodological quality. Indeed, methodological aspects such as the study population, data collection, curve modeling and others are of crucial importance for the final outcome of the process. Beside the discussion on methodological issues, there is also an ongoing discussion regarding whether one international standard might be adequate to assess fetal growth all around the globe, or are there some differences related to ethnicity supporting the adoption of growth charts constructed based on national data, or even the customization.

Recently, the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) Practice Guidelines on Ultrasound Assessment of Fetal Biometry and Growth recommended the application of "prescriptive biometry charts, obtained prospectively, truly population-based and derived from studies with the lowest possible methodological bias", and called for the practitioners' awareness regarding national or even local reference charts. Such awareness requires an exploratory and preliminary analysis of the impact of different charts by applying reference values to local findings.

A recent multicentric Italian study promoted by the Italian Society of Ultrasound in Obstetrics and Gynecology (SIEOG), assessed the application of WHO growth charts published in 2006 and the Intergrowth 21 (IG-21st) growth charts in a large Italian cohort (n=7347) of low risk women with uneventful pregnancy. According to the results of the study the IG-21st standards identified the smallest proportion of fetuses below the 10th centile and the largest proportion of fetuses above the 90th centile, respectively. The proportion of fetuses with head circumference (HC), abdominal circumference (AC) and femur length (LF) above 90th centile was 29.9%, 32.5 and 46%, respectively. While the WHO references seem to be the closest to observed 10th centile, the proportion of fetuses above 90th centile was also higher than expected for an appropriate distribution of centiles, but smaller compared with IG-21st standards: 22.8%, 21.3% and 31.9% for HC, AC and LF, respectively. Overall, these data suggest that there might be differences linked to ethnic origin and not fully explained by maternal, socio-economic or other methodological factors as already suggested by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and World Health Organization (WHO) groups.

These data suggest that, despite indisputable advantages that IG-21st growth standards might offer, immediate application into clinical practice might result into an under-diagnosis of small for gestational age fetuses and, especially, in an over-diagnosis of large for gestational age fetuses with major consequences for clinical practice. The WHO growth references seem to be more suitable for our population, although they might also over-estimate the proportion of large for gestational age fetuses. On the other hand, existing national growth charts lack crucial biometric parameters and centiles. This is of major importance, if we consider that recent consensus criteria suggested AC and estimated fetal weight (EFW) below the 3rd centile as independent criteria for the diagnosis fetal growth restriction.

On these grounds, there is an urgent need for a nationwide study for the prospective collection of data and the construction of methodologically robust national growth and Doppler standards.