Pregnant with Hypothyroidism? Increase Your Medication!

Researchers Find Thyroid Hormone Needs Increase During Early Pregnancy

Happy pregnant woman holding belly
B2M Productions/Photographer's Choice RF/Getty Images

If you’re pregnant and hypothyroid, you may need an increase in your dose of thyroid hormone replacement, even just a few weeks after conception, according to research reported in the New England Journal of Medicine.

The study, conducted at Brigham and Women’s Hospital-Harvard Medical School in Boston, found that 85 percent of pregnant women with hypothyroidism --a condition where the thyroid is unable to produce sufficient thyroid hormone -- require an increase in thyroid hormone replacement drug to protect the baby.

Babies born to mothers with undertreated hypothyroidism are at increased risk of including cognitive problems and stillbirth.

"Hypothyroidism during pregnancy has been associated with impaired cognitive development and increased fetal mortality," wrote Erik K. Alexander, MD, from the Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, and colleagues. "During pregnancy, maternal thyroid hormone requirements increase. Although it is known that women with hypothyroidism should increase their levothyroxine dose during pregnancy, biochemical hypothyroidism occurs in many."

19 women who were planning to become pregnant were evaluated prior to becoming pregnant, and then every two weeks during pregnancy. In 17 out of 20 women, they needed an increase in their thyroid dose, and the mean level of increase was 47 percent, at eight weeks into the pregnancy.

Interestingly, the body's increased demand for levothyroxine during pregnancy was seen as early as the fifth week of gestation, leading the researchers to recommend that women themselves raise their thyroid drug intake immediately upon confirming pregnancy.

According to the study authors: “We suggest that women with hypothyroidism be instructed to increase their usual levothyroxine intake by two additional doses each week immediately on confirmation of pregnancy and to contact their healthcare provider so that a program of test-guided dose adjustments can be instituted.”


Remember to take any vitamins with iron (most prenatal vitamins have iron in them) at least 4 or more hours apart from your thyroid hormone.

Taking them too close together may interfere with your thyroid drug's effectiveness.

Be careful about calcium supplements, calcium-fortified orange juice, and antacids that contain calcium. They should be taken at least 4 or more hours apart from your thyroid hormone. Taking them too close together may interfere with your thyroid drug's effectiveness.


For more tips and information on how to manage your hypothyroidism to have a healthy baby, and a healthy you, read the Thyroid Guide to Fertility, Pregnancy and Breastfeeding Success.

Source: Alexander, Erik K. M.D., et. al. Timing and Magnitude of Increases in Levothyroxine Requirements during Pregnancy in Women with Hypothyroidism, New England Journal of Medicine, Volume 351:241-249 July 15, 2004, Number 3 Online: