Implications for quantifying early life growth trajectories of term‐born infants using INTERGROWTH‐21st newborn size standards at birth in conjunction with World Health Organization child growth standards in the postnatal period

Abstract Background The INTERGROWTH‐21st sex and gestational age (GA) specific newborn size standards (IG‐NS) are intended to complement the World Health Organization Child Growth Standards (WHO‐GS), which are not GA‐specific. We examined the implications of using IG‐NS at birth and WHO‐GS at postnatal ages in longitudinal epidemiologic studies. Objectives The aim of this study was to quantify the extent to which standardised measures of newborn size and growth are affected when using WHO‐GS versus IG‐NS at birth among term‐born infants. Methods Data from two prenatal trials in Bangladesh ( n = 755) and The Gambia ( n = 522) were used to estimate and compare size at birth and growth from birth to 3 months when using WHO‐GS only (‘WHO‐GS’)…