Total T4 concentrations are stable throughout pregnancy at 150% of pre-pregnant values, and are considered more reliable than Free T4 Estimate tests when evaluating pregnant patients, as long as the levels are evaluated according to a pregnancy-specific Total T4 reference range (~85 to 240 nmol/L / ~7 to 19 g/dL, i.e. 1.5 times the non-pregnant reference range).
What This Means For You?
If you're a thyroid patient who is pregnant, you will want to make sure that your primary care doctor or obstetrician is aware of this information regarding appropriate tests and pregnancy TSH levels. Many experts recommend that you are tested within the first six weeks of conception, a period when thyroid needs expand greatly. You should also be tested again during your first trimester, and at least once during each subsequent trimester, or more often if levels are not normalizing with treatment.
Sources: Spencer, et. al. "Thyroid Function Tests & Pregnancy: What's Normal?" Endocrine Society Annual Meeting, May 2005. Abstracts: S7-1
The Thyroid Guide to Fertility, Pregnancy, and Breastfeeding Success, by Mary Shomon
Mary Shomon, About.com's Thyroid Guide since 1997, is a nationally-known patient advocate and best-selling author of 10 books on health, including the "Thyroid Guide to Fertility, Pregnancy and Breastfeeding Success," the New York Times best-seller "The Thyroid Diet: Manage Your Metabolism for Lasting Weight Loss," "Living Well With Hypothyroidism: What Your Doctor Doesn't Tell You...That You Need to Know," "Living Well With Graves' Disease and Hyperthyroidism," and "Living Well With Autoimmune Disease," "Living Well With Chronic Fatigue Syndrome and Fibromyalgia." Click here for more information on Mary Shomon.
