Prematurity may be a risk factor for thyroid dysfunction in childhood

Context: Children born prematurely and/or small for gestational age (SGA) frequently show disturbances in thyroid function. Objective: The objective of the study was to determine the role played either by size or gestational age on subsequent thyroid function. Design and Setting: This cross-sectional study was conducted at a tertiary referral hospital. Patients: A total of 117 children, 88 of whom were SGA (mean age 7.8 +/- 2.5 yr) and 29 appropriate for gestational age (AGA) (mean age 8.1 +/- 1.9 yr), were selected for the study. Main Outcome Measures: We evaluated TSH, free T(4), free T(3), urinary iodine, and antithyroid antibodies, and all patients underwent a thyroid ultrasound. Insulin sensitivity was assessed with the quantitative insulin sensitivity check index. Results: TSH and free T(3) were not significantly different in the two groups, whereas free T(4) was higher in the AGA group (P < 0.005). Interestingly, four AGA (13.8%) and 17 SGA (19.3%) patients had TSH levels above the upper limit of normality. Thyroid volume was normal and thyroid autoimmunity was excluded. Urinary iodine was also similar in the two groups (115 +/- 66 vs. 143 +/- 87); however, in both groups there were some children [15 AGA (51%) and 13 SGA (14.7%) (P < 0.001)] with a mild to moderate iodine deficiency. By multiple regression analysis, gestational age was found to be the only determinant of TSH serum levels. Insulin sensitivity was the same in both groups of children and similar to controls. Conclusions: Some children born prematurely, independently from their birth size, frequently have disturbances of the hypothalamus-pituitary-thyroid axis later in life.