Jansen TA, et al. - In this prospective cohort study, researchers explored how maternal thyroid function impacts child brain morphology and if the timing of thyroid evaluation influences that relationship. Participants were pregnant women living in Rotterdam with an expected delivery date from April 1, 200, to January 1, 2006. Maternal serum thyroid-stimulating hormone (TSH) and free thyroxine (FT 4) measurement in early or mid-pregnancy (≤18 weeks) and available brain MRI data for child at age 10 years were other inclusion criteria. Investigators found that both low and high maternal thyroid function were linked to smaller child total grey matter and cortical volume. This study is the first to demonstrate that by measuring maternal thyroid function early in pregnancy, association with a neurodevelopmental outcome is most evident. These new findings suggest that the development of the embryonic brain is especially susceptible to altered maternal thyroid function.