"No benefit” to treating mild low thyroid in pregnancy

Treating women with mildly low thyroid function during pregnancy may be of no benefit, according to a new US study.

Although markedly low thyroid function during pregnancy is known to be associated with impaired fetal neurological development and increased risk for preterm birth and miscarriage, research that suggested even mildly low thyroid function (subclinical hypothyroidism) could possibly affect a newborn’s cognitive development and increase the chances for pregnancy and birth complications was limited.

The latest large, long-term study found no differences in cognitive functioning among children born to mothers with subclinical hypothyroidism who were treated with medication during pregnancy and children whose mothers were not treated for the condition. In addition, no differences were between the groups in rates of preterm birth, stillbirth, miscarriage and gestational diabetes.

“Our results do not support routine thyroid screening in pregnancy since treatment did not improve maternal or infant outcomes,” said study author Dr Uma Reddy, of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Pregnancy and Perinatology Branch.

Thyroid hormone levels of more than 97,000 women were tested before the 20th week of pregnancy, over a three-year period. Women in the study were screened for elevated levels of thyroid stimulating hormone (TSH) — an indicator of reduced thyroid function—but normal levels of the thyroid hormone thyroxine (T4). They also were screened for lower levels of T4 — another potential marker of reduced thyroid function—but normal levels of TSH.


Researchers randomly assigned 677 women with mildly elevated levels of TSH to receive treatment with the drug levothyroxine (a synthetic form of T4) or a placebo.  Additionally, 526 women with mildly low T4 levels were randomized to receive the drug or a placebo. Children born to women in all the groups underwent IQ testing and were assessed by child development specialists each year until they were five years of age.

Researchers found no significant differences between the treated and untreated groups in pregnancy complications, such as gestational diabetes or preeclampsia (high blood pressure during pregnancy). Among newborns, there were no differences in rates of stillbirth, death, birthweight, or respiratory problems. Similarly, there were no differences in the results of developmental assessments between the two groups of children through age five.

The researchers say the study results confirm those of earlier studies. The study was carried out by a National Institutes of Health research network and published in the New England Journal of Medicine. See link here: http://www.nejm.org/doi/full/10.1056/NEJMoa1606205

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