Is there an association between thyrotropin levels within the normal range and birth growth parameters in full-term newborns?

Abstract

It has been suggested that thyroid hormone concentration at birth may have some role in regulating foetal growth. The aim of this study was to provide seminal data regarding any association between thyrotropin (TSH) concentration within the normal range and growth parameters at birth in full-term newborns. In this cross-sectional study conducted in Tehran, Iran, 314 mother-newborn pairs were randomly selected from health care centres responsible for congenital hypothyroidism screening. Neonatal TSH concentration was measured using a heel-prick blood sample taken from all neonates 3-5 days after birth, as part of the routine neonate screening. Anthropometrics, including birth weight, length and head circumference were obtained from the birth record of each neonate. The z-score values for weight-for-age, weight-for-length, length-for-age and head-for-age were calculated using the World Health Organisation growth standards. The median interquartile range neonatal TSH values were 0.9 mIU/L (0.4-1.7 mIU/L). Neonates in the top tertile of TSH values had higher birth weights and weight-for-age z-scores than those in the bottom tertile (p<0.05). In addition, neonatal TSH was associated with weight-for-age z-scores in unadjusted (β=0.113, p=0.020) and adjusted (β=0.122, p=0.013) analysis. However, in both unadjusted and adjusted analysis, no association was observed between TSH concentrations of neonates and weight-for-length, length-for-age and head-for-age z-scores. Our findings indicate a positive association between the normal range of neonatal screening TSH concentration and birth weight; however, this association was not observed for other anthropometric parameters at birth.