Thyroid Hormone Function in Small for Gestational Age Term Newborns

Abstract

To test the hypothesis that term-born small for gestational age (SGA) neonates have elevated thyroid-stimulating hormone (TSH) concentrations and an increased incidence of congenital hypothyroidism compared with non-SGA term neonates. This retrospective cohort study included all term neonates screened in Wisconsin in 2015 and 2016. The cohort was divided based on SGA status, defined as birth weight <10th percentile as calculated from the World Health Organization's sex-specific growth charts for age 0-2years. TSH concentration on first newborn screening performed between birth and 96hours of life and incidence of congenital hypothyroidism were compared between the SGA and non-SGA groups. A total of 115 466 term neonates, including 11 498 (9.96%) SGA neonates, were included in the study. TSH concentration and incidence of congenital hypothyroidism was significantly higher in the SGA group, but only TSH concentration remained significant when adjusted for potential confounding variables. Our data do not support a higher incidence of congenital hypothyroidism in term SGA neonates after adjusting for potential confounders. However, TSH concentrations were higher in term SGA neonates compared with term non-SGA neonates. The effects of mild thyroid hormone dysfunction on neurodevelopmental outcomes and development of chronic medical conditions merit long-term study.