Thyroglobulin as an evolving biomarker of iodine reserve in thyroid dysfunction assessment in pregnancy

Background: Despite the use of routine thyroid function tests, thyroid dysfunction is often missed in pregnant women, who may have fluctuating iodine reserves and this may be associated with an increased risk of adverse maternal and fetal outcomes due to thyroid dysfunction. Therefore, thyroglobulin (Tg) as a marker of iodine reserve may be added to improve the diagnostic value of the thyroid testing panel. Materials and Methods: This study was a multicenter descriptive cross-sectional study with 501 healthy pregnant women, carried out over 9 months, in which blood and urine (spot) specimens were collected and analysed for serum thyroid-stimulating hormone, free thyroxine, free triiodothyronine, and Tg using enzyme-linked immunosorbent assay, and urinary iodine concentration by modified Sandell–Kolthoff reaction. Results: The prevalence of thyroid dysfunction in pregnant women using thyroid function tests alone was 12.4% (62) with 9.6% (48) being hypothyroid and 2.0% (10) hyperthyroid. The addition of Tg was able to identify more participants with thyroid dysfunction who were iodine deficient, and initially missed using thyroid function tests alone. This newly added biomarker to routine thyroid function tests profile increased the prevalence of thyroid disorders in this study population from 12.4% (62) to 17.6% (88) (P < 0.01), whereas urine iodine concentration was adequate for each trimester falling within the WHO range of 150–249 μg/l. Conclusion: The true prevalence of thyroid dysfunction in pregnant women in Makurdi was 17.6%. The addition of Tg had an impact on thyroid function tests by identifying more participants with iodine-related thyroid dysfunction, who were missed in the initial assessment of the thyroid. The mean urine iodine concentration was adequate, falling within the WHO range of 150–249 μg/l.