Levie D, Korevaar TIM, Bath SC, et al. - Via analyzing data from three prospective population-based birth cohorts: Generation R (Netherlands), INMA (Spain), and ALSPAC (United Kingdom), researchers recruited pregnant women between 2002 and 2006, 2003 and 2008, and 1990 and 1992, respectively, to explore the connection between maternal iodine status during pregnancy and child IQ and identify vulnerable time windows of exposure to suboptimal iodine availability. Study participants included 6,180 mother-child pairs with measures of urinary iodine and creatinine concentrations in pregnancy and child IQ. The data presented in this work showed a positive curvilinear relationship of urinary iodine/creatinine ratio (UI/Creat) with mean verbal IQ only. UI/Creat < 150 µg/g was not related to lower nonverbal IQ or lower verbal IQ. Stratified analyses found that UI/Creat's correlation with verbal IQ was present only for up to 14 weeks of gestation. It was concluded that fetal brain development, especially in the first trimester, is vulnerable to mild to moderate iodine deficiency. Results indicate that potential randomized controlled trials evaluating the impact of iodine supplementation in women with mild to moderate iodine deficiency on child neurodevelopment will begin supplementation no later than the first trimester.