A study recently published by the Journal of Clinical Endocrinology and Metabolism looked at the connection between TSH levels and pregnancy outcomes in hypothyroid women being treated with thyroid hormone replacement medication, in this case, the synthetic T4 medication levothyroxine.
The study, which evaluated more than 50,000 hypothyroid women, found that during the first trimester, almost 63% of the women had a TSH level above 2.5 mU/L, which is the recommended upper limit for TSH during the first trimester. More than 7% had a TSH over 10 mU/L. The women with a TSH above 4.51 had an increased risk of miscarriage, compared to women with the targeted first trimester TSH levels of .2 - 2.5 mU/L.
The researchers concluded that "there is an urgent need to improve the adequacy of thyroid hormone replacement in early pregnancy." And their recommendation was that it is reasonable to aim for a serum TSH near 1.0 at the time of conception (excluding women with thyroid cancer) to potentially improve pregnancy outcomes.
What This Means for Hypothyroid Women?
If you are hypothyroid and considering getting pregnant, here are some important tips to consider:
- Make a pre-conception appointment with your doctor, at least three months before you plan to get pregnant. At that time, your doctor can check your thyroid levels, and adjust your thyroid hormone replacement medication dosage if necessary to aim for the target TSH of 1.0 mU/L. (Note: some thyroid cancer patients are maintained at lower TSH levels, known as "suppression," to prevent thyroid cancer recurrence.) The doctor may also recommend that you take a pre-natal vitamin that includes folic acid (which helps prevent neural tube defects), and iodine, which is necessary.
- Confirm your pregnancy as early as possible. For women with thyroid disease, it's not wise to wait until you miss a period to take a pregnancy test. Some physicians recommend you start testing as early as a week after possible conception. Note: Many fertility experts suggest that the "First Response" brand pregnancy test is particularly sensitive, and its manufacturer claims it's highly accurate as early as six days before your expected period.
- Have a plan with your doctor to raise thyroid medication levels as soon as your pregnancy is confirmed. Most women need as much as a 50% increase in their dosage during the first trimester - when the baby's neurological development depends entirely on the mother's thyroid hormone production. Your physician should instruct you on exactly how much thyroid medication to add as soon as your pregnancy is confirmed, as well as when to first get your thyroid levels rechecked after becoming pregnant.
Once you're pregnant, you'll want to have your thyroid levels monitored regularly throughout the pregnancy, so that your dosage of medication can be periodically adjusted. According to the 2011 "Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum," your TSH level should not exceed 2.5 mU/L during your first trimester, and 3.0 during the second and third trimesters.
Source: Mestman, Jorge, et. al. "Levothyroxine-Treated Women in Their Reproductive Years Should Have their Serum TSH Adjusted Before Conception to Prevent Hypothyroidism in the First Trimester." Journal of Clinical Endocrinology and Metabolism, Epub ahead of print, July 24, 2014 Online