Optimization of the follow-up of pregnant women with autoimmune thyroid disease

To determine the risk of hypothyroidism in pregnant women with autoimmune thyroid disease and thyrotropin (TSH) < 2,5 mIU/l at the beginning of pregnancy.

Prospective longitudinal study of pregnant women with no personal history of thyroid disease, and with TSH < 2.5 mIU/l in the first trimester. TSH, free thyroxine (FT4), anti peroxidase (TPO) and anti thyroglobulin antibodies were measured in the 3 trimesters of pregnancy. We compared thyroid function throughout pregnancy, and the development of gestational hypothyroidism (TSH >4 mIU/l) among pregnant women with positive thyroid autoimmunity and those with negative autoimmunity.

We included 300 pregnant women with mean baseline TSH 1.3 ± 0.6 mIU/l (9^th gestational week). Positive thyroid autoinmunity was detected in 17.7% of women (n = 53) at the first trimester. Between the first and the third trimesters, TPO and anti thyroglobulin antibodies titers decreased 76.8% and 80.7% respectively. Thyroid function during pregnancy was similar among the group with positive autoimmunity and the group with negative autoimmunity, and the development of hypothyroidism was 1.9% (1/53) and 2% (5/247) respectively. Pregnant women in whom TSH increased above 4 mIU/l (n = 6), had higher baseline TSH levels compared to those who maintained TSH ≤4 mIU/l during pregnancy (1.8 vs. 1.3 mIU/l; p=.047).

In our population, women with TSH levels <2.5 mIU/l at the beginning of pregnancy have a minimal risk of developing gestational hypothyroidism regardless of thyroid autoimmunity.