Customized versus population-based birth weight standards for identifying growth restricted infants: A French multicenter study

Objective This study was undertaken to describe the characteristics of pregnancies according to a customized definition of fetal growth restriction and to determine the association between customized standards and adverse pregnancy outcomes. Study design Two definitions of growth restriction, a population and a customized standard, were applied to 56,606 births in 5 tertiary maternity hospitals in France from 1997 to 2002. The customized definition was adjusted for maternal height and weight, parity, fetal gender, and gestational age. Odds ratios and 95% CIs for neonatal morbidity and mortality were calculated to compare small for gestational age and non-small for gestational age births. Results By using customized standards, 2.7% of births were reclassified as small for gestational age. These births were to taller, heavier, multiparous women. Compared with non-small for gestational age births, these newly detected small-for-gestational-age newborn infants showed an increased risk of stillbirth (odds ratio = 4.52, 95% CI 2.47-8.14) and perinatal death (odds ratio = 2.60, 95% CI 1.62-4.15). These infants were also more likely to be born to women with hypertensive disease in pregnancy (7.0%) versus those reclassified as non-small for gestational age (2.3%) and those non-small for gestational age by both standards (5.5%). Conclusion These findings highlight the interest of using customized birth weight standard adjusted for maternal and neonatal characteristics to identify fetuses at risk, particularly among apparently normal fetuses. Individual growth norms should be used to define small for gestational age.