Effect of Maternal Iodine Excess during Pregnancy on Neonatal Thyroid Function and Neurodevelopmental Status at 12 Weeks

Abstract

Objective. This study aims to determine the effect of iodine excess in pregnant mothers on thyroid function, growth and neurodevelopment in the neonates when assessed at 12 weeks of age. Methodology. This prospective study enrolled term neonates with birth weight >2500 gm of mothers having urine iodine concentration (UIC) ≥500 µg/L documented in the third trimester of the peripartum period. Neonatal TSH was collected by heel prick on dried blood spots within 24-72 hours of age and measured by time-resolved fluroimmunoassay. Neonates with TSH ≥11 mIU/L at birth were followed up at 2 and 12 weeks to monitor thyroid dysfunction, growth and development. Results. A total of 2354 (n = 1575 in the delivery room) maternal urine samples were collected of which 598 (25.4%) had elevated UIC. Forty-nine (12.2%) neonates had TSH ≥11mIU/L on newborn screening of whom 18 and 3 neonates had residual elevated TSH at 2 and 12 weeks of life, respectively. Maternal iodine levels correlated weakly with TSH at 2 weeks (rho = 0.299; p = 0.037). No child required treatment for congenital hypothyroidism. Eight babies additionally had TSH >5 mIU/L at 12 weeks of life. The growth and development of babies with or without TSH elevation was comparable at three months (p >0.05). Conclusion. Maternal iodine excess in pregnancy and peripartum period causes transient hyperthyrotropinemia in neonates that did not affect the growth and development at 3 months of age.

Keywords

• thyroid
• hypothyroidism
• iodinization
• hyperthyrotropinemia
• thyroid function test
• urine iodine concentration