Fetal brain development might be hampered by mild to moderate maternal iodine deficiency, especially in the first trimester, according to study results published in The Journal of Endocrinology & Metabolism.

To evaluate how iodine levels in pregnant women influence child IQ and determine at what point fetuses could be most susceptible to maternal iodine deficiency, researchers conducted a meta-analysis of 6180 mother-child pairs from 3 prospective population-based birth cohorts (Generation R [Netherlands], Infancia y Medio Ambiente Project [Spain], and Avon Longitudinal Study of Parents and Children [United Kingdom]). Each pair was measured for maternal urinary iodine and creatinine concentrations during pregnancy, and data for verbal and nonverbal child IQ were available from each cohort.

Median urinary iodine/creatinine ratio was 159 μg/L (adequate intake) in the Generation R cohort, 128 μg/L (mild deficiency) in the Infancia y Medio Ambiente cohort, and 96 μg/L (moderate deficiency) in the Avon Longitudinal Study of Parents and Children cohort; iodine status was calculated for each cohort at a median gestational age of 13.1, 13, and 12 weeks, respectively.

Although a positive linear association between urinary iodine/creatinine ratio and mean nonverbal IQ was deemed nonsignificant, the researchers discovered a positive and statistically significant curvilinear association between urinary iodine/creatinine ratio and mean verbal IQ. Neither a ratio <150 μg/g nor ≥500 μg/g was associated with lower nonverbal IQ (-0.6 points; P =.246) or lower verbal IQ (-0.6 points; P =.082).

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Furthermore, in the first 12 weeks of gestation, there was a positive curvilinear association between mean child verbal IQ and urinary iodine/creatinine ratio, with an overall effect of approximately 5 IQ points and an effect of approximately 3 IQ points between 12 and 14 weeks. After 14 weeks, this association ceased to exist.

Study limitations included the use of different tools to assess child IQ in each cohort.

In summarizing their findings, the researchers said, “this study confirms that iodine status in pregnancy is associated with child IQ and results indicate that the development of verbal IQ of the fetus is particularly vulnerable to suboptimal iodine concentration during early pregnancy up until the start of [the] second trimester.”

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Levie D, Korevaar TIM, et al. Association of maternal iodine status with child IQ: a meta-analysis of individual-participant data [published online March 28, 2019]. J Clin Endocrinol Metab. doi:10.1210/jc.2018-02559