Information Information for professionals Overt hypothyroidism in conception and pregnancy What is overt hypothyroidism? Overt hypothyroidism is defined as having a Thyroid Stimulating Hormone (TSH) greater than 10 mU/L with a free thyroxine (FT4) level below the reference range. What are the risks? If it is untreated, or inadequately treated, it may be harder for women to become pregnant, and their pregnancy may be at higher risk. These risks include premature birth, low birth weight, pregnancy loss, and problems with the baby’s brain development. How should it be treated? Women with overt hypothyroidism should be given levothyroxine treatment with the aim of preventing abnormal thyroid function tests and mimicking normal physiological changes. This will give them the best chance of becoming pregnant, having a successful pregnancy and a healthy baby. Before pregnancy Women’s care should be managed by their GP. Adjust levothyroxine dose if needed to achieve adequate pre-conception TSH <2.5 mlU/L. Ideally, check thyroid function every six months while trying to get pregnant. During pregnancy Counsel to self-initiate an empirical increase in their dose of levothyroxine by 20-30% as soon as they have a positive pregnancy test. This can be achieved by doubling the dose of levothyroxine on 2 days of each week. Test thyroid function as soon as their pregnancy is confirmed, ideally by 7-9 weeks of pregnancy. TSH should be <2.5 mlU/L and FT4 should be in the normal manufacturer-specific pregnancy-specific range. Adjust dose when TSH approaches the upper end of the normal range. Aim for TSH in lower half of pregnancy-specific range. Refer to an endocrinologist/obstetrician. Check thyroid function every 4-6 weeks until 20 weeks, then once again at 28 weeks. After birth Reduce levothyroxine to pre-pregnancy dose 2 weeks after birth. Check thyroid function, usually during 6-week postnatal check. Note: If there are no pregnancy-specific ranges available, use the TSH range 0.1-4.0mU/L. Read the RCOG Green-top guideline on the Management of Thyroid Disorders in Pregnancy Manage Cookie Preferences Please ensure Javascript is enabled for purposes of website accessibility