The effect of iodine supplementation in mildly iodine-deficient pregnant women on child development: a 5-year follow-up of the MITCH Study
Zimmermann, Michael B.
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Rationale: Severe iodine deficiency during pregnancy increases the risk of adverse pregnancy outcomes, and impairs motor and cognitive performance in the offspring. Inadequate thyroid hormone supply to the fetus is the likely cause. In contrast, the potential adverse effects of mild iodine deficiency during pregnancy are less clear, as controlled trials of iodine supplementation in mildly iodine deficient pregnant women do not increase concentrations of maternal or newborn thyroid hormones. Moreover, there are no long-term data from controlled trials in mildly iodine deficient pregnant women that have measured the effect of iodine supplementation on infant or child development. Objective: The study aim is to determine whether daily oral iodine supplementation in pregnant women with mild iodine deficiency improves cognitive development of their offspring 4 to 5 years postpartum. Study design: The study is a long-term follow-up of the children of pregnant women who completed a randomized placebo controlled trial of iodine supplementation –the MITCH (Maternal Iodine Supplementation and its Effects on Thyroid function and CHild Development) study– in 2009-2010. The children and their families will be invited to the health clinic where they will answer a socio-demographic questionnaire and complete a dietary assessment of iodine intake. Their height and weight will be measured, and a spot urine sample will be collected for measurement of urinary iodine, and a blood spot from a finger prick will be collected for measurement of thyroid hormones. The children will be tested with the WIPPS and the BRIEF-P to assess cognitive development. Co-primary outcomes are the verbal and performance IQ scores from the WPPSI and the global executive composite score from the BRIEF-P. In addition, because iodine deficiency in utero may be associated with hearing deficits, which in turn may affect cognitive development, we will also assess auditory function by measuring hearing threshold by using optoacoustic emissions. Study population: Healthy pregnant women, gestational age ≤14 weeks, from two sites (in Bangkok, Thailand and in Bangalore, India) were randomized to receive either a daily supplement of 200 μg oral iodine or placebo from enrollment until delivery. Women were followed through delivery, and then with postnatal follow-up of their infants at 6 weeks, 12 and 24 months. Infant development was assessed using the Neonatal Behavioral Assessment Scale (NBAS) at 6 weeks of age and using the Bayley Scales of Infant Development (BSID III) at 1 and 2 years. At 2 years, the BRIEF (Behavior Rating Inventory of Executive Function)-P was also done in India. There were no significant group differences in the BSID III scores at 1 and 2 years of age at either site, and no significant group differences in the NBAS in Thailand. However, in India, iodine had small but significant benefits on the NBAS at 6 weeks and the BRIEF-P measured at 2 years. The pooled data from the two sites is now being analyzed. The children in the study are now 4 to 5 years old, and developmental tests in children at 4-5 years of age are more robust, reliable and predictive of life-long intelligence than tests given during infancy. Main study parameters/endpoints: The primary study outcome is the difference in scores on the WIPPS and BRIEF-P between intervention groups, with the verbal and performance IQ scores from the WPPSI and the global executive composite score from the BRIEF-P as co-primary outcomes. Secondary outcomes will be scores on the Strengths and Difficulties questionnaire, as well as auditory function, urinary iodine concentrations (UIC), thyroid function indicators (TSH, TT4), weight and height. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The burden and risks associated with participation are negligible. The follow up study will require the children to undergo cognitive and auditory testing (half-day) and their mothers to answer questionnaires related to their children. Children will be asked to hand in a spot urine sample to assess iodine concentration, and a capillary blood spot to assess haemoglobin, thyroid stimulating hormone and free thyroxine concentrations (not obligatory for participation). Parents of children with strongly deviating results (e.g. low intellectual capacity, deafness, anaemia or hypothyroidism) will be informed and referred for treatment, which is a benefit of participation in the follow up study. Whether it is beneficial to supplement mildly iodine deficient pregnant women with iodine is uncertain. WHO does not recommend supplementation in areas with well-functioning iodized salt programs, while many expert medical groups recommend supplementation in areas of mild iodine deficiency. This is the first randomized controlled trial that will assess the longterm effect on child development of iodine supplementation of mildly iodine deficient pregnant women. It will therefore provide important evidence to inform optimized guidelines on iodine supplementation of this group. Show more
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Edition / version3
Organisational unit03957 - Zimmermann, Michael / Zimmermann, Michael
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