Congenital hypothyroidism in Indian preterm babies – screening, prevalence, and aetiology

Introduction
Paucity of data on hypothyroidism in Indian preterms. Aim of the study: To describe the prevalence, aetiology, and experience with screening for primary hypothyroidism in preterm babies.

Material and methods
A prospective observational study conducted for 3 years in a tertiary care unit, where all babies born < 37 weeks screened by heel prick for Thyroid Stimulating Hormone (TSH) were included. All screen positive cases (TSH ≥ 6 µIU/ml) underwent venous testing immediately; venous TSH ≥ 20 or Free T4 < 0.9 ng/dl was considered as confirmed positive. All babies underwent venous testing at term. Etiological testing was performed where feasible. Confirmed cases were initiated on thyroxine therapy and followed up.

Results
1167 preterm babies presented during the study period. 1147 (98%) underwent TSH screening and 17 (1.4%) were screen positive; 15 babies underwent confirmatory venous test. Of these 15 babies, 2 were confirmed and started on therapy. The remaining 13 babies underwent retest venous sample at term, and 8 of these were confirmed cases. Of the screen-negative babies, 94% underwent repeat venous testing at term/ prior to discharge. Five were confirmed to have congenital hypothyroidism. Thus, the prevalence of congenital hypothyroidism was 1 in 77 preterm babies. No correlation was observed between screening TSH and venous TSH (p > 0.05). Aetiological evaluation in 8 babies revealed secondary to maternal antibody in 4 cases (50%) and permanent thyroid defects in 4 cases (50%).

Conclusions
We observed a high prevalence (1 in 77), need for repeat venous testing, irrespective of initial screening, and significant permanent congenital hypothyroidism (50%) in our series.