The second wave of the Controlled Antenatal Thyroid Screening (CATS II) study: the cognitive assessment protocol.

BACKGROUND: Children whose mothers had low thyroid hormone levels during pregnancy have been reported to have decreased cognitive function. The reported research is part of the follow-on study of the Controlled Antenatal Thyroid Screening Study (CATS I), a randomised controlled trial which investigated the impact of treated vs. untreated low thyroid hormone level in women during pregnancy with the primary outcome being the child's IQ at age 3. No significant differences in IQ were found between the treated and untreated groups. These children are now aged between 7 and 10 years and aspects of their cognitive functioning including their IQ are being reassessed as part of CATS II. METHODS/DESIGN: Cognitive assessments generate an IQ score and further tests administered will investigate long term memory function and motor coordination. The aim is to complete the assessments with 40% of the children born to mothers either in the treated or untreated low thyroid hormone groups (n = 120 per group). Also children born to mothers who had normal thyroid functioning during CATS I are being assessed for the first time (n = 240) to provide a comparison. Assessments are conducted either in the research facility or the participant's home. DISCUSSION: The study is designed to assess the cognitive functioning of children born to mothers with low thyroid hormone levels and normal thyroid functioning during pregnancy. This is the largest study of its type and also is distinguishable in its longitudinal design. The research has the potential to have a significant impact on public health policy in the UK; universal screening of thyroid hormone levels in pregnancy may be the recommendation.

CATS II Long-term Anthropometric and Metabolic Effects of Maternal Sub-optimal Thyroid Function in Offspring and Mothers.

CONTEXT AND OBJECTIVES: The Controlled Antenatal Thyroid Screening Study I (CATS-I) was a randomized controlled trial investigating the effects of levothyroxine therapy for suboptimal gestational thyroid function (SGTF), comparing outcomes in children of treated (SGTF-T) with untreated (SGTF-U) women during pregnancy. This follow-up study, CATS-II, reports the long-term effects on anthropometric, bone, and cardiometabolic outcomes in mothers and offspring and includes a group with normal gestational thyroid function (NGTF). DESIGN & PARTICIPANTS: 332 mothers (197 NGTF, 56 SGTF-U, 79 SGTF-T) aged 41.2±5.3 years (mean±SD) and 326 paired children assessed 9.3±1.0 years after birth for (i) body mass index (BMI); (ii) lean, fat, and bone mass by dual-energy X-ray absorptiometry; (iii) blood pressure, augmentation index, and aortic pulse-wave-velocity; and (iv) thyroid function, lipids, insulin, and adiponectin. The difference between group means was compared using linear regression. RESULTS: Offspring's measurements were similar between groups. Although maternal BMI was similar between groups at CATS-I, after 9 years (at CATS-II) SGTF-U mothers showed higher BMI (median [interquartile ratio] 28.3 [24.6-32.6] kg/m2) compared with NGTF (25.8 [22.9-30.0] kg/m2; P = 0.029), driven by fat mass increase. At CATS-II SGTF-U mothers also had higher thyroid-stimulating hormone (TSH) values (2.45 [1.43-3.50] mU/L) than NGTF (1.54 [1.12-2.07] mU/L; P = 0.015), since 64% had never received levothyroxine. At CATS-II, SGTF-T mothers had BMI (25.8 [23.1-29.8] kg/m2, P = 0.672) and TSH (1.68 [0.89-2.96] mU/L; P = 0.474) values similar to NGTF mothers. CONCLUSIONS: Levothyroxine supplementation of women with SGTF did not affect long-term offspring anthropometric, bone, and cardiometabolic measurements. However, absence of treatment was associated with sustained long-term increase in BMI and fat mass in women with SGTF.