TPO and Miscarriage: An association between circulating thyroid peroxidase antibodies (TPOAb) and miscarriage has been found by a number of observational studies and confirmed by a recent meta-analysis [1] (Thyroid peroxidase is an enzyme that helps produce the thyroid hormones T3 and T4, by liberating iodine so it can be added to tyrosine residues on thyroglobulin).