The identification of newborns who present an abnormality of intrauterine growth remains problematic, both from the multi-factorial aspect of fetal growth and from the statistical definition of this abnormality. Besides the usual terms, "Small for gestational age" and IUGR often used synonymously; the Anglo-Saxon litterature has recently introduced the term "Fetal Growth Restriction" (FGR) referring to infants who failed to achieve their "genetic growth potential" in utero.

From a sample of approximately 50,000 births from the AUDIPOG database (97 712 pregnancies between 1999 and 2001), we have developped a birth weight and birth height modelling taking into account gestational age, birth rank and sex of the infant as well as maternal height and weight. Thanks to this modelling, we are able to calculate an individual limit of birth weight or height under which a newborn must be considered as having suffered a "Fetal weight growth restriction" (and / or Fetal height growth restriction ) (FwGR versus FlGR).
This new approach allows us to classify some newborns in "constitutionally small" due to their low growth potential and to identify 2 groups of newborns with FwGR: one classically identified as SGA (noted FwGR I) (3,9 %), and the other one newly identified as FwGR (noted FwGR II) (1,4 %). That's why 20% of infants with FwGR went unnoticed and, on the contrary 20 % of "SGA" infants were "actually misclassified".

Reference : MAMELLE N, COCHET V, CLARIS O. Definition of fetal growth restriction according to constitutional growth potential. Biol Neonate 2001 ; 80:277-285.