The following is a summary of “Evaluating the Progression to Hypothyroidism in Preconception Euthyroid Thyroid Peroxidase Antibody–Positive Women,” published in the January 2023 issue of Endocrinology & Metabolism by Gill, et al.

Thyroid dysfunction, especially hypothyroidism, which has negative consequences on pregnancy, is predisposed to thyroid peroxidase antibody (TPOAb) positive, which is common in women of reproductive age. For a study, researchers sought to compare the outcomes of euthyroid and treated hypothyroid people, as well as to describe the rate of development of aberrant thyroid function among originally euthyroid TPOAb-positive women recruited into the TABLET experiment.

In the observational cohort study, which took place at 49 UK hospitals between 2011 and 2016, euthyroid TPOAb-positive women between the ages of 16 and 40 who were planning pregnancy and had a history of miscarriage or infertility were randomly assigned to receive levothyroxine 50 mcg daily or a placebo. Analysis was done on the live birth rate (LBR) at ≥34 weeks, abnormal thyroid function, and conception rate.

About 70/940 (7.3%) of the women had subclinical (SCH) or overt (OH) hypothyroidism, with 27/470 receiving levothyroxine and 43/470 receiving a placebo (relative risk [RR] 0.63; 95% CI, 0.39-1.00; P = 0.05); 83% of instances occurred prior to conception. In individuals who acquired hypothyroidism compared to those who did not, baseline median blood TSH concentrations and TPOAb titers were considerably greater (P< 0.001). Comparing treated SCH/OH to euthyroid women, a greater failure-to-conceive rate was seen (adjusted RR 2.02 [1.56-2.62]; P< 0.001). The LBR ≥ 34 weeks was comparable in the treated SCH/OH and euthyroid groups (adjusted RR 1.09 [0.77-1.55]; P = 0.6).

In the year before conception or during pregnancy, 7% of euthyroid TPOAb-positive women would develop hypothyroidism. Compared to euthyroid women, conception rates were lower in women with treated SCH/OH, but LBR was comparable. When attempting to get pregnant, TPOAb-positive women should have their thyroid function periodically checked to ensure quick diagnosis and effective therapy start.