High prevalence of thyroid dysfunction in pregnant women

Background/Aim: Maternal thyroid dysfunction during pregnancy has been associated with adverse obstetric and neonatal outcomes. This prospective study evaluates the prevalence of these disorders in pregnant women. Subjects and methods: Serum levels of TSH, free T4 (fT4), and thyroperoxidase antibodies (TPO-Ab) were measured in 951 women at different gestational ages of pregnancy. Trimester-specific reference ranges for TSH were used to classify pregnant women into five groups: 1) Overt hypothyroidism (OH); 2) Subclinical hypothyroidism (SCH); 3) Isolated hypothyroxinemia (IH); 4) Low TSH (isolated or associated with high fT4); and 5) Normal. A classification was made also according to the lower and upper ranges provided by the manufacturer for thyroid hormones. Pregnant women who were at a high risk of developing thyroid disease were identified. Results: Altogether, 117 women (12.3%) had hypothyroidism and 25 (2.6%) had low TSH. The prevalence of both OH and SCH was higher in the high-risk group than in the low-risk group, but 17.9% of women with hypothyroidism were classified at low-risk. A family history of thyroid disorders and TPO-Ab positivity increased the risk of SCH. Using non-pregnant reference range for TSH, 10.6% of women were misclassificated. Conclusions: The high prevalence of hypothyroidism observed in this study suggests that accurate thyroid screening with trimester specific reference ranges should be warranted, particularly in areas with mild to moderate iodine deficiencies.