Endocrine Abstracts

Low thyroid function in pregnancy is associated with adverse obstetric outcomes but it is unclear whether screening and initiation of levothyroxine during pregnancy is beneficial. The Controlled Antenatal Thyroid Study (CATS) was a randomised controlled trial which screened women for low thyroid function (subclinical hypothyroidism and isolated hypothyroxinemia) between 11 and 16 weeks gestation. CATS provides data on obstetric outcomes and offspring neurological development. These data are key to the crucial debate as to whether universal thyroid screening in pregnancy is beneficial. The original trial assessed offspring IQ at age 3, a follow on study (CATS II) assessed IQ and other cognitive outcomes at age 9. Obstetric outcomes were obtained using data-linkage from the Secure Anonymised Information Linkage databank. The original CATS study found no difference in mean IQ between treated and untreated women with low thyroid function. Mean IQ scores were 99.2 and 100.0 in the screening and control groups, respectively (difference=0.8; 95%CI (−1.1 −2.6) P=0.40. The proportions of children with an IQ of less than 85 were 12.1% in the screening group and 14.1% in the control group P=0.39. Similar results were seen at age 9. Children of ‘over-treated’ mothers displayed more ADHD symptoms than women with normal thyroid function. Potential benefits were seen in preventing fetal loss. Untreated women with low thyroid function had higher odds of fetal loss than women with normal thyroid function OR=9.61 (95%CI 5.03, 18.4) P<0.001. Untreated individuals also had a higher odds of miscarriage than those who received treatment OR =4.07 (95%CI 1.14, 14.5) P=0.03. No clear differences were seen for other obstetric outcomes. Screening for and treating low thyroid function at the end of the first trimester does not appear to improve neurological outcomes, however it may have a role in preventing fetal loss. Over-treatment should be avoided with monitoring.