Language delay and poorer school performance in children of mothers with inadequate iodine intake in pregnancy: results from follow-up at 8 years in the Norwegian Mother and Child Cohort Study.

PURPOSE: Some studies indicate that mild-to-moderate iodine deficiency in pregnant women might negatively affect offspring neurocognitive development, including previous results from the Norwegian Mother and Child Cohort study (MoBa) exploring maternally reported child development at age 3 years. The aim of this follow-up study was to investigate whether maternal iodine intake in pregnancy is associated with language and learning at 8 years of age. METHODS: The study sample includes 39,471 mother-child pairs participating in MoBa with available information from a validated food frequency questionnaire covering the first half of pregnancy and a questionnaire on child neurocognitive development at 8 years. Multivariable regression was used to explore associations of iodine intake from food and supplements with maternally reported child outcomes. RESULTS: Maternal iodine intake from food less than ~ 150 µg/day was associated with poorer child language skills (p-overall = 0.013), reading skills (p-overall = 0.019), and writing skills (p-overall = 0.004) as well as poorer school test result in reading (p < 0.001), and increased likelihood of the child receiving special educational services (p-overall = 0.042) (in non-iodine supplement users). Although significant, differences were generally small. Maternal use of iodine supplements in pregnancy was not significantly associated with any of the outcomes. CONCLUSIONS: Low habitual iodine intake in pregnant women, i.e., lower than the recommended intake for non-pregnant women, was associated with mothers reporting poorer child language, school performance, and increased likelihood of special educational services. We found no indications of benefits or harm of using iodine-containing supplements in pregnancy. Initiating use in pregnancy might be too late.

Maternal Iodine Status is Associated with Offspring Language Skills in Infancy and Toddlerhood.

Inadequate iodine status affects the synthesis of the thyroid hormones and may impair brain development in fetal life. The aim of this study was to explore the association between maternal iodine status in pregnancy measured by urinary iodine concentration (UIC) and child neurodevelopment at age 6, 12 and 18 months in a population-based cohort. In total, 1036 families from nine locations in Norway were enrolled in the little in Norway cohort. The present study includes n = 851 mother-child pairs with singleton pregnancies, no use of thyroid medication in pregnancy, no severe genetic disorder, data on exposure (UIC) in pregnancy and developmental outcomes (Bayley Scales of Infant and Toddler Development, third edition). Data collection also included general information from questionnaires. We examined associations between UIC (and use of iodine-containing supplements) and repeated measures of developmental outcomes using multivariable mixed models. The median UIC in pregnancy was 78 µg/L (IQR 46⁻130), classified as insufficient iodine intake according to the WHO. Eighteen percent reported use of iodine-containing multisupplements. A UIC below ~100 was associated with reduced receptive (p = 0.025) and expressive language skills (p = 0.002), but not with reduced cognitive or fine- and gross motor skills. Maternal use of iodine-containing supplements was associated with lower gross motor skills (b = -0.18, 95% CI = -0.33, -0.03, p = 0.02), but not with the other outcome measures. In conclusion, an insufficient iodine intake in pregnancy, reflected in a UIC below ~100 µg/L, was associated with lower infant language skills up to 18 months. The use of iodine-containing supplements was not associated with beneficial effects.

Suboptimal Maternal Iodine Intake Is Associated with Impaired Child Neurodevelopment at 3 Years of Age in the Norwegian Mother and Child Cohort Study.

Background: Severe iodine deficiency in pregnancy has major effects on child neurodevelopment, but less is known about the potential consequences of mild-to-moderate deficiency and iodine supplement use.Objective: We explored the associations between maternal iodine intake and child neurodevelopment at 3 y of age and the potential impact of maternal intake of iodine from supplements on the same outcomes.Methods: This population-based prospective observational study included 48,297 mother-child pairs recruited during pregnancy from 2002 to 2008. Maternal iodine intake was calculated based on a validated food-frequency questionnaire answered during midpregnancy that covered mean intake since the beginning of pregnancy. Associations between iodine intake and maternal-reported child language and motor development and behavior problems were explored by multivariable regression analyses.Results: In 33,047 mother-child pairs, excluding iodine supplement users, maternal iodine intake was associated with child language delay (P = 0.024), externalizing and internalizing behavior problems (both P < 0.001), and fine motor skills (P = 0.002) but not gross motor skills or the risk of not walking unaided at 17 mo of age. In 74% of the participants who had an iodine intake <160 µg/d (Estimated Average Requirement), suboptimal iodine intake was estimated to account for ∼5% (95% CI: -5%, 14%) of the cases of language delay, 16% (95% CI: 0%, 21%) of the cases of externalizing behavior problems >1.5 SD, and 16% (95% CI: 10%, 21%) of the cases of internalizing behavior problems >1.5 SD. In 48,297 mother-child pairs, including iodine supplement users, we found no protective effects of supplemental iodine during pregnancy on neurodevelopment.Conclusions: Maternal iodine intake below the Estimated Average Requirement during pregnancy was associated with symptoms of child language delay, behavior problems, and reduced fine motor skills at 3 y of age. The results showed no evidence of a protective effect of iodine supplementation during pregnancy.