Low thyroid function during pregnancy doesn’t threaten expecting mothers or their babies, according to new findings published in The New England Journal of Medicine. The report challenges previous research associating hypothyroidism with impaired fetal brain development and increased risk for preterm birth and miscarriage, reports the National Institutes of Health (NIH).
Low thyroid function, or hypothyroidism, is a common disorder that occurs when the thyroid gland doesn’t produce enough thyroid hormone. The thyroid gland is a small butterfly-shaped organ at the front of the neck that secretes hormones that affect growth, metabolic function and many other cellular processes throughout the body. Signs of the disorder include weight gain, fatigue and swelling—which makes hypothyroidism particularly difficult to diagnose during pregnancy without a specific test.
For the study, researchers tested the thyroid hormone levels of more than 97,000 women in 15 centers of the NIH’s Maternal Fetal Medicine Units Network before their 20th week of pregnancy. Women in the study were screened for elevated levels of thyroid stimulating hormone (TSH), a common indicator of low thyroid function, as well as lower levels of T4, another potential marker for hypothyroidism.
Next, scientists randomly assigned 677 pregnant women with mildly elevated levels of TSH to receive treatment with the drug levothyroxine (a synthetic from of T4) or a placebo. Additionally, 526 women with mildly low levels of T4 were randomized to receive the hormone treatment or a placebo. Children born to women in all the groups underwent IQ testing, and a child development specialist assessed the kids each year through age 5.
Findings showed no significant differences between the treated and untreated mothers with regard to their likelihood for pregnancy complications, such as gestational diabetes or preeclampsia (high blood pressure during pregnancy). Among newborns, there were also no differences between the groups in rates of stillbirth, death, low birth weight or respiratory issues. Similarly, through age 5, there was no difference in the IQ scores or cognitive development between the children of those women who received thyroid treatment during pregnancy and those who did not.
“Our results do not support routine thyroid screening in pregnancy, since treatment did not improve maternal or infant outcomes,” said Uma Reddy, MD, of the National Institute of Child Health and Human Development (NICHD) at the NIH, a study author. (These study results confirmed those of an earlier trial that screened about 22,000 women and followed their infants until age 3.)
The findings support recent research on thyroid disease and show why doctors are concerned about overtreating the disorder. Click here for more information.