Effect of maternal age, height, BMI and ethnicity on birth weight: an Italian multicenter study

To assess the effect of maternal age, height, early pregnancy body mass index (BMI) and ethnicity on birth weight.

A cross-sectional study was conducted on more than 42,000 newborns. Ethnicity was defined by maternal country of birth or, when missing (<0.6% of records), by citizenship. The effect of maternal characteristics on birth weight was evaluated with general linear models.

Maternal height and BMI, although not age, significantly affected birth weight. Among Italian babies, 4.7% of newborns were classified as appropriate-for-gestational age (AGA) (birth weight between the 10th and the 90th centile) according to the country-specific Italian Neonatal Study (INeS) charts and were re-classified as either large-(LGA) (birth weight >90th centile) or small-(SGA) (birth weight <10th centile) for gestational age (GA) after adjustment for maternal characteristics. On the contrary, 1.6% of Italian newborns were classified as SGA or LGA according to the INeS charts and re-classified as AGA after adjustment. Maternal ethnicity had a significant impact on birth weight. Specifically, babies born to Senegalese mothers were the lightest, whilst babies born to Chinese mothers were the heaviest.

Maternal height and early pregnancy BMI, should be considered in the evaluation of birth weight. The effect of ethnicity suggests the appropriateness of ethnic-specific charts. Further studies are necessary to determine if changes in birth weight classification, may translate into improved detection of subjects at risk of adverse outcomes.