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.