Endocrine Abstracts

Hypothyroidism before and during pregnancy has been linked with adverse pregnancy outcomes. Observational studies have demonstrated that thyroid autoimmunity, characterised by the presence of thyroid peroxidase (TPO) antibodies, is associated with increased risks of miscarriage and pre-term birth. Small trials indicated that levothyroxine therapy could reduce such adverse outcomes, but the evidence was inconclusive. The TABLET trial is a multicentre, double-blind, placebo-controlled randomized trial to investigate whether levothyroxine treatment could increase live birth among euthyroid women with thyroid antibodies. Women were randomly assigned to receive 50 mcg per day of levothyroxine or placebo, commenced preconception and continued until the end of pregnancy. Women were given a twelve month period to conceive and the primary outcome was live birth at ³ 34 weeks gestation. 19,585 women were tested for thyroid antibodies and thyroid function across 49 UK hospitals. The overall prevalence of abnormal thyroid function was 4.8% (95% CI 4.5–5.1) and was overt in 0.4% (0.3–0.6) and subclinical in 3.6% (3.4–3.9). TPOAb positivity was found in 9.5% (9.1–9.9)) and was associated with euthyroidism in more than 90%. Women with higher BMI, subfertility and Asian ethnitiy were more likely to have thyroid dysfunction and autoimmunity. Using a lower (2.5 mIU/l) cut-off for serum TSH resulted in significantly increased rates of subclinical hypothyroidism (19.9% (19.3–20.5) vs 3.6% (3.4–3.9) for TSH >4.5 mIU/l). A total of 1420 women were eligible for the trial, of whom 952 were randomly assigned to receive either levothyroxine (476) or placebo (476). At the time of writing of this abstract the final outcomes are being analysed. We have identified specific subgroups of women at risk of thyroid dysfunction or autoimmunity in whom levothyroxine replacement may be beneficial. It is anticipated that the final outcomes of the TABLET trial will be available by the time of this presentation.