Gestational thyroid function abnormalities in conditions of mild iodine deficiency: early screening versus continuous monitoring of maternal thyroid status

Abstract

Objective: To longitudinally evaluate the timing of maternal thyroid underfunction occurrence in mildly iodine-deficient (ID) pregnant women, and ultimately assess the benefit of thyroid function testing at early gestation only in identifying maternal thyroid underfunction. Participants/methods: Serum free-thyroxine and TSH were measured in 220 consecutive women once in early pregnancy (by week 12) and twice per trimester subsequently. Anti-thyroperoxidase and antithyroglobulin were also determined at initial and final observation. Results: Thyroid autoantibodies were detectable in 8.2% women. Overall, the prevalence of hypothyroidism over the course of gestation was 11.8% (26/220), with a relative risk of hypothyroidism in antibody-positive women of 5.0 (c 2 20.02, P!0.0005). Nonetheless, almost 70% hypothyroid women tested negative for thyroid autoantibodies. Fifteen/26 (57.7%) hypothyroid women were identified at presentation, and the remaining 11 at either early (6/11) or late (5/11) phases of the 2nd trimester. Isolated hypothyroxinemia was observed in 56/220 (25.4%) women, mostly from the 2nd trimester onwards. Conclusions: In mildly ID areas thyroid function testing early in gestation seems to be only partly effective in identifying thyroid underfunction in pregnant women. Indeed, in our series more than 40% hypothyroid women would not have been diagnosed had we limited our observation to early thyroid function tests alone. Although thyroid autoimmunity carried a 5-fold increased risk of hypothyroidism, iodine deficiency seems to be a major determinant in the occurrence of thyroid underfunction. Adequate iodine supplementation should be strongly recommended to meet the increased hormone demand over gestation.

Treatment and screening of hypothyroidism in pregnancy: results of a European survey

“…One could argue that the identification and treatment of hypothyroidism in the first antenatal visit, as recommended by the guidelines (4, 7), may be too late to prevent the associated adverse effects; however, implementing systemic screening of thyroid function in all women contemplating pregnancy would be an enormous challenge for any country. Although a recent study has suggested that, if screening is limited to first trimester, over 40% pregnant women with hypothyroidism could be missed (19), there was no agreement amongst responders whether thyroid function tests should be routinely repeated in later stages of pregnancy if the initial screening was normal.…”

Universal screening detects two-times more thyroid disorders in early pregnancy than targeted high-risk case finding

“…the variables measured and their cut-off values, are more controversial (16). In addition, the yield of screening may be influenced by regional differences, namely, by iodine sufficiency (25).…”

Screening and management of hypothyroidism in pregnancy: Results of an Asian survey

“…One could argue that the identification and treatment of hypothyroidism in the first antenatal visit may be too late to prevent the associated adverse effects; however, implementing systemic screening of thyroid function in all women contemplating pregnancy would be an enormous challenge, especially for developing countries of Asia. A recent study has suggested that, if screening is limited to first trimester, over 40% of pregnant women with hypothyroidism could be missed [12] and 68% of our responders agreed that thyroid function tests should be repeated in later stages of pregnancy if the initial screening was normal, 27% routinely and 41% in the presence of thyroid antibodies.…”

“…countries with ten or more responders included: Iran (44), Indonesia (43), Philippines (40), Taiwan (38), Malaysia (23), Japan (14), Singapore (12), India (11), Thailand (11), and Srilanka (10).…”