Thyroid antibodies are associated with an increased risk of miscarriage and premature delivery, even when thyroid function is normal. The TABLET trial was a randomised, double-blind, placebo-controlled trial to investigate whether treatment with levothyroxine would increase live-birth rates among euthyroid women who had positive peroxidase antibodies and a history of miscarriage or infertility.

The conclusions were that the use of levothyroxine in euthyroid women with peroxidase antibodies did not result in a higher rate of live births. Details of the results of the trial are published in an article in the New England Journal of Medicine. https://www.nejm.org/doi/full/10.1056/NEJMoa1812537 

More information is available on the TABLET trial website.