Definition of fetal growth restriction according to constitutional growth potential

Identification of newborn babies with fetal growth restriction remains a problem both from the multi-factorial aspect of fetal growth and from statistical definition. Besides the usual terms: "Small for gestational age" (SGA) and intrauterine growth retardation (IUGR), often used synonymously, the term "fetal growth retardation" was recently introduced in reference to the genetic growth potential of infants. From a sample of 72,000 births, we have designed a statistical model in order to estimate the expected birth weight taking into account gestational age, sex, birth rank, maternal age, height and pregravid weight, we then calculated an individual limit of birth weight under that a newborn must be considered as having a "fetal growth restriction" quoted FwGR. This new approach allowed us to identify 2 groups of newborns with FGR, one classically identified as SGA (noted FwGR(I)) (3.9%), and the other newly identified as FGR (noted FwGR(II)) (1.4%). In contrast, this approach allowed us to identify a group of "constitutionally small" infants according to their constitutional growth potential (1.1%). In other words, among infants usually defined as SGA (5%), 22% appeared in fact to be "constitutionally small" and therefore misclassified. As an initial validation, we observed that the proportion of maternal hypertension during pregnancy was low in the "constitutionally small" infants (close to that of the normal group), and three times higher in the newly identified group FwGR(II) than in the normal group. Following these results, it seems to be meaningful to follow-up this new group of FwGR(II) infants, in terms of catch-up growth and neurodevelopmental outcome.