My daughter is 19 and has had all her thyroid tissue removed due to tumor growths. She is taking 250mg of synthroid. What effect would this have on getting pregnant? Will synthroid harm a fetus?

Elaine

The doses of synthroid are micrograms (mcg) not milligrams (mg). A synthroid dose of 250mg is more than 1,000 times more than regularly prescribed and would likely be fatal! But even if the dose is 250mcg, that is still quite high. Rarely is a dose higher than 150-200mcg necessary to restore normal thyroid function. A dose that is higher than necessary may increase the risk of osteoporosis as well as miscarriage and irregular menses.

The adequacy of the synthroid dose is determined by measuring levels of thyroid stimulating hormone (TSH). The goal of medical treatment is to keep this pituitary-stimulating hormone in the normal range. Think of TSH as gasoline to the thyroid engine. If you are already going fast enough because of the synthroid, the TSH drops into the normal range. If the synthroid dose is too high, your pituitary gland "takes its foot off the gas," and the TSH level can fall to very low levels.

Your daughter should discuss this with her physician. Regular checks of TSH are a part of any infertility evaluation.