Thyroid function and thyroid autoimmunity in apparently healthy pregnant and non-pregnant Mexican women.

Background: Thyroid disorders are common in women of reproductive age, and thyroid dysfunction during pregnancy has been associated with adverse outcomes for mother and child. Thyroid function and thyroid function tests (TFTs) can be influenced by a variety of factors, such as ethnicity, the presence of autoimmune thyroid disease (AITD), dietary iodine intake, pregnancy, and methodological differences. However, no large-scale studies have been published which examine TFTs and prevalence of AITD in Mexican pregnant women and women of reproductive age.

Methods: TFTs and thyroid autoantibody testing were performed on 660 pregnant and 104 non-pregnant women from Mérida, Yucatán, Mexico. After removal of thyroid autoantibody positive individuals and women with thyroid stimulating hormone (TSH) >4.94 mIU/L, reference intervals were calculated for TFT for non-pregnant women and pregnant women by trimester.

Results: Anti-thyroidperoxidase antibodies (TPO-Ab) and/or anti-thyroglobulin antibodies (Tg-Ab) were positive in 14.4% and 13.5% of non-pregnant and pregnant women, respectively. TSH values were significantly higher in women who were positive for TPO-Ab and co-positive for TPO-Ab and Tg-Ab. TSH values were also significantly higher in Tg-Ab positive pregnant women. Other TFTs were not significantly different based on antibody status. Using antibody negative women, reference intervals were determined for TFTs in pregnant (gestational age-specific) and non-pregnant women.

Conclusions: Laboratory evidence of AITD is common in this population of Mexican pregnant and non-pregnant women. TFT results and reference intervals are influenced by pregnancy and thyroid autoimmunity. For optimal interpretation of TFT results, gestational age-specific reference intervals established using a local patient population should be used.