Major Finding: Generalized screening and treatment of pregnant women for hypothyroidism does not improve intellectual outcomes for their offspring.
Data Source: CATS randomized almost 22,000 pregnant women to screening and treatment for hypothyroidism or no screening. At age 3, the children of treated women were intellectually comparable to those of nontreated women.
Disclosures: The trial was funded by the U.K. Wellcome Trust. Dr. Lazarus had no financial conflicts to declare.
PARIS — Screening pregnant women for hypothyroidism and treating them early in pregnancy doesn't seem to improve their children's intellectual development.
The preliminary results of the CATS (Controlled Antenatal Thyroid Screening) trial, presented at the congress, found no differences in the intellectual development of 3-year-olds whose hypothyroid mothers took levothyroxine during pregnancy and those who did not take the hormone, said primary investigator Dr. John Lazarus.
“At the moment, I think we have data that argues against population-based screening and treatment for these women,” he said in an interview. “This leaves the decision of whether to screen and treat up to the individual physician. The Endocrine Society guidelines, so far, say that testing should only be done in early pregnancy if there is some significant risk factor. But other studies show that if you adopt this method, you miss a significant number of women who should be treated.”
CATS is the first large-scale randomized controlled trial to tackle the issue. An earlier study (N. Engl. J. Med. 1999; 341:549–55) was retrospective, so it could not draw any direct conclusion about causation, said Dr. Lazarus, professor of clinical endocrinology at the University Hospital Wales and Cardiff University.
He presented preliminary data on the CATS study population comprising nearly 22,000 women with singleton pregnancies whose blood was tested for free thyroxine (T4) and thyroid stimulating hormone before 16 weeks' gestation. Before being tested, the sera were randomized to either screening (10,923) or control (10,198). Women in the screening group with low T4 and/or high TSH were given 150 mcg/day levothyroxine, and those in the control group with these results were given the drug after delivery.
Among the screening group, 4.7% were found to be hypothyroid and received treatment. Among the control group, 3.6% were found to be hypothyroid, a statistically nonsignificant difference.
When the children of these women were aged 38–40 months, they underwent intellectual testing. Dr. Lazarus presented data on 404 children in the control group and 390 in the screening group.
In the intention-to-treat analysis, the investigators found no difference in the mean IQ scores of children randomized to screening or no screening (100 vs. 99). Nor was there a significant between-group difference in the percentage of children with an IQ of less than 85 (11.5% in the screening group vs. 15.6% in the control group).
A subgroup analysis found a different result, however. The investigators examined results only among women whose consecutive blood levels showed that they were compliant with their medication. In this analysis, the mean IQ was still similar (100 vs. 100), but the percentage of those with an IQ below 85 became significantly different (9.5% screening group vs. 15.6% control group).
Dr. Lazarus cautioned against using this finding as a case for population screening, however. “By looking at it that way, we are no longer looking at a randomized group, so this is why these are very preliminary data,” he said.