Despite the vast literature attesting to the powerful effects of retinoic acid (RA) on embryogenesis and cell physiology, there is no appreciable understanding of association between gene variations in vitamin A pathway and nephron numbers. Retinoic acid levels in the embryo could be affected by several factors such as maternal vitamin A status and genes that are involved in vitamin A metabolism, transport or activity. Thus, it’s critical to understand how the genetic variations in vitamin A metabolism pathway affect the nephron numbers and also whether these variants may modify associations between maternal dietary vitamin A intakes on risk for low nephron numbers. We propose to genotype each newborn for vitamin A pathway alleles previously associated with reduced newborn kidney size in a North American population (RETrs11190688, RALDH2rs71692899) or with decreased cord retinoic level29,38 (RBP4rs11187540, CRABP2rs12724719, RALDH2rs12591551, STRA6rs17852249) and look for an association between these polymorphic variants and (a) shift in newborn kidney size and function and (b) shift in umbilical cord RA concentration.