Objective: To determine thyrotropin (TSH) and thyroid hormones reference ranges in healthy term newborns during the neonatal period and to assess the ranges of thyroid volume in newborns using ultrasound scanning.
Methods: Blood samples were collected from 296 healthy newborns at birth (cord; n: 47) and before feeding on the 1st, 3rd, 5th, 7th, 10th, 14th, and 28th days of life. The levels of TSH and thyroid hormones of the newborns were then compared with results from 50 healthy adults. Thyroid ultrasonography (USG) was performed by the same radiologist on 38 newborns aged 10 days.
Results: TSH and thyroid hormone levels in newborns were statistically higher than those in adults for each day (p < 0.001). Serum TSH concentration on the 1st day of life was higher than at other times (p < 0.001). Mean TSH concentration reverted to the cord level at the 5th or 7th day of life (p > 0.05). TSH levels were no higher than 10 mIU/ml after 2 weeks postnatal age. There was no correlation between hormone levels and Ponderal index (PI), birth weight, gender, or delivery type. Mean thyroid volume was 0.72 ± 0.24 ml (0.36-1.62 ml).
Conclusions: We conclude that our results are important for CH screening regarding time-dependent changes of TSH and thyroid hormones besides diagnosis of thyroid hypoplasia or hyperplasia.