How should a woman with hypothyroidism be treated during pregnancy?
The treatment of hypothyroidism in a pregnant woman is adequate replacement of thyroid hormone in the form of synthetic levothyroxine (see Hypothyroidism brochure). Ideally, hypothyroid women should have their levothyroxine dose optimized prior to becoming pregnant and should have their thyroid function tested as soon as pregnancy is detected. Levothyroxine requirements frequently increase during pregnancy, often times by 25 to 50 percent, so the dose should be adjusted by their physician as needed to maintain a TSH in the normal range. It is also important to recognize that prenatal vitamins contain iron that can impair the absorption of levothyroxine from the gastrointestinal tract. Consequently, levothyroxine and prenatal vitamins should not be taken at the same time and should be separated by at least 2-3 h. Thyroid function tests should be checked approximately every 6-8 weeks during pregnancy to ensure that the woman has normal thyroid function throughout pregnancy.
