(HealthDay News) – Screening for maternal hypothyroidism, and treatment of women with positive results, is not associated with improved IQ in offspring at age 3, according to a study published in the Feb. 9 issue of the New England Journal of Medicine.

John H. Lazarus, M.D., from the Cardiff School of Medicine in the United Kingdom, and colleagues investigated whether antenatal screening and treatment for hypothyroidism was associated with improved cognitive outcomes in offspring at 3 years of age. A total of 21,846 women, with a median gestational age of 12 weeks and 3 days, provided blood samples for which thyrotropin and free thyroxine levels were measured immediately (screening group) or shortly after birth (controls). Women in the screening group who tested positive were treated with levothyroxine. IQ of the child was measured by psychologists at age 3.

The investigators found positive results for hypothyroidism in 390 women in the screening group and 404 in the control group. Treatment with levothyroxine was started in those in the screening group at a median gestational age of 13 weeks and 3 days. The mean IQ scores among children of women with positive results were 99.2 in the screening group and 100.0 in the control group (P=0.40 by intention-to-treat analysis). The proportion of children with an IQ of <85 was 12.1% and 14.1% in the screening and control groups, respectively (P=0.39).

“Current guidelines do not recommend routine antenatal screening for hypothyroidism in pregnancy. Our study provides support for these guidelines, since we found no benefit of routine screening for maternal hypothyroidism at about 12 to 13 weeks’ gestation in the prevention of impaired childhood cognitive function,” the authors write.

One of the study authors disclosed financial ties to the pharmaceutical industry.

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