Normalized Weight of Iranian Newborns According to Gestational Age: A Nationwide Study.

Background: By organizing birth weights according to gestational age at birth, reference weight values for different sex-gestational ages are provided.

Methods: Data of 1,090,779 mothers and their neonates were gathered from 30 provinces of Iran. Pregnancy complications, maternal risk factors, type of delivery, maternal outcome, neonatal sex and APGAR score were determined. Birth weights were quantified into 3rd, 50th and 97th centile. Regression analysis was used to estimate birth weight of neonates.

Results: Birth weight showed an enhancing trend with age; boys weighed more, multiparous women had higher neonatal birth weight, mothers with cardiovascular disease and diabetes mellitus had heavier infants, and mothers aged below 20 years had lower estimated infant birth weight. Gestational age (beta = 147.3) and male sex (beta = 114.9) were the most important independent variables, respectively for predicting birth weight (R-square = 0.512 and P < 0.001). In other words, with each unit increase in gestational age, birth weight would increase by 147.3 grams. Male fetuses were also 114.9 grams heavier than females of the same gestational age. Value of R-square shows relatively acceptable goodness of this statistical model.

Conclusion: A national reference for fetal growth patterns and related factors was determined in this study.