Endocrine Abstracts

Introduction: Mild iodine deficiency in the Faroe Islands raises a concern for pregnant women. Iodine is essential for thyroid hormone synthesis, making it crucial for thyroid function during pregnancy and foetal growth. World Health Organization (WHO) classifies iodine intake in pregnant women as insufficient if the median urinary iodine concentration (UIC) is below 150 µg/l. We investigated how UIC relates to thyroglobulin (Tg) and thyroid-stimulating hormone (TSH) in serum as markers of thyroid activity.

Method: This was a cross-sectional study with longitudinal aspects in the Faroe Islands. We recruited 645 Faroese pregnant women early in the second trimester from June 2020 to April 2022 for blood and spot urine samples. UIC was measured in spot urine using the Sandell-Kolthoff reaction modified according to Wilson and van Zyl. TG measurements were conducted in 143 randomly selected participants. Serum Tg and TSH were measured using immunoassays (BRAHMS and Alinity I; Abbott).

Results: Overall, the median UIC was 110 µg/l and the median TSH was 1.23 mIU/l. There were 32 participants with UIC <50 µg/l, for whom we also had corresponding Tg values. For the entire group, 61 participants had UIC <50 µg/l regardless of Tg presence. Serum Tg levels were higher in the group with UIC <50 µg/l (n=32) compared to those with UIC from 50-100 µg/l or above. On the other hand, neither serum Tg nor TSH differed between groups of pregnant women with UIC of 50-99 vs 100-149 vs 150-299 µg/l, but TSH was slightly lower with UIC <50 µg/l (median 1.09 mIU/l (n=61)) and higher with UIC >300 µg/l (median 1.51 mIU/l (n=42)).

Conclusion: Among pregnant women in the Faroe Islands, TSH was similar between groups of pregnant women with UIC in the range from 50-300 µg/l. Similarly, serum Tg was raised only in the group with UIC below 50 µg/l. Results suggest that the lower limit of UIC recommended by WHO in pregnancy may be too strict when evaluated according to markers of thyroid activity.