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

OBJECTIVE

Contradictory 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.

DESIGN

Based 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.

METHODS

Two thousand five hundred and ninety-five twin pairs that were screened both for TSH and thyroxine (T(4)) over 3 years were included. TSH and T(4) levels were evaluated along with BW, birth order, gender, and 17-hydroxyprogesterone (17OHP) that was considered as a surrogate marker for stress.

RESULTS

Of all the twin pairs, 7.2% had neonatal HT. Among 156 pairs, HT was more prevalent in the smaller twins (64%; P<0.001), especially in the discordant pairs (76%; P=0.001). Seventy-five percent of the twins demonstrated a recovery within the first few weeks of life. 17OHP levels were similarly distributed between twins with and without HT. In a cohort of 1534 twin pairs with normal thyroid function, mean TSH levels were significantly higher in the smaller than in the larger twin in the whole group (4.1±3.2 vs 3.8±2.9 mIU/l; P<0.001) and especially among discordant twins (4.7±3.4 vs 3.8±3.0 mIU/l; P<0.001).

CONCLUSIONS

Elevated TSH levels are associated with low BW, both in infants with HT and in normal neonates. A rapid recovery rate is expected in most cases.