Neonatal hyperthyrotropinemia is associated with low birth weight: a twin study

ObjectiveContradictory reports ascribe neonatal hyperthyrotropinemia (HT) to prematurity or small weight for gestational age. We aimed to evaluate the association between neonatal HT and birth weight (BW), recovery rate of the disorder, and possible association with perinatal stress.DesignBased on a neonatal screening database, a retrospective twin study was designed where within-pair differences in thyroid function were evaluated while controlling for differences in gestational age and thyroid-affecting environmental confounders.MethodsTwo thousand five hundred and ninety-five twin pairs that were screened both for TSH and thyroxine (T4) over 3 years were included. TSH and T4 levels were evaluated along with BW, birth order, gender, and 17-hydroxyprogesterone (17OHP) that was considered as a surrogate marker for stress.ResultsOf all the twin pairs, 7.2% had neonatal HT. Among 156 pairs, HT was more prevalent in the smaller twins (64%; P