Endocrine Abstracts

Background and aims: Thyroid peroxidase antibody (TPOAb) positivity is prevalent in women of reproductive age and pre-disposes to thyroid dysfunction, namely hypothyroidism, which has adverse effects on pregnancy. The aim of this study was to report the rate of development of abnormal thyroid function among initially euthyroid TPOAb positive women recruited into TABLET trial. To also identify factors associated with the development of hypothyroidism and to compare outcomes between euthyroid and treated hypothyroid individuals.

Methods: This was an observational cohort study across 49 UK hospitals between 2011-2016. Participants were euthyroid TPOAb-positive women aged 16-40years with a history of miscarriage or subfertility planning pregnancy, randomized to levothyroxine 50 mg daily or placebo. The main outcome measures were abnormal thyroid function, conception rate and live birth (LBR) ≥34weeks.

Results: A total of 70/940 (7.4%) TPOAb-positive women developed subclinical (SCH) or overt (OH) hypothyroidism: 27/470 taking levothyroxine and 43/470 on placebo (relative risk (RR) 0.63; 95%CI 0.39-1.00;P=0.05); 83% of cases emerging pre-pregnancy. Baseline mean serum TSH concentrations were higher in those who developed hypothyroidism compared to those who did not (TSH 2.66mIU/l vs 2.05mIU/l;P<0.001). Treated SCH/OH demonstrated a higher failure-to-conceive rate compared to euthyroid women (adjusted RR 2.02 [1.56-2.62]; P<0.001). The LBR ≥34weeks was similar in the treated SCH/OH and euthyroid groups (adjusted RR 1.09 [0.77-1.55];P=0.6).

Conclusions: Approximately 7% of euthyroid TPOAb-positive women will develop hypothyroidism within 1year preconception, or in pregnancy. Conception rates are lower in women with treated SCH/OH compared to euthyroid women, but live birth rates are comparable. Thyroid function in TPOAb-positive women should be monitored regularly, when trying to conceive, to ensure prompt diagnosis and appropriate treatment initiation.