They excluded multiple pregnancies, use of fertility treatment, known thyroid disease, or use of medications that could affect the thyroid. Since the measurements were done by different methods researchers used techniques to standardize the values so they were able to compare 3 different groups.
The study included 6180 mother-child pairs. Urine samples were collected around 12-14 weeks of pregnancy. Urine iodine-to-creatinine ratios were used to assess mother’s iodine status. Urine iodine-to-creatinine ratios were 159 mcg/L in the group from The Netherlands (iodine sufficient), 128 mcg/L in the group from Spain (mildly iodine deficient) and 96 mcg/L in the United Kingdom group (moderately iodine deficient). Associations between iodine status and child verbal IQ were seen during the first 12 weeks but not after 14 weeks of pregnancy. Urine iodine-to-creatinine ratios were not associated with the child’s non-verbal IQ or mother’s TSH or free T4 levels.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that lower urinary iodine-to-creatinine ratios up to 14th week of pregnancy were associated with poorer child verbal IQ scores. This is important to patients because timing of iodine supplementation may be critical for the development of baby’s language ability. The American Thyroid Association recommends women who are planning pregnancy, pregnant, or lactating should take 150 mcg of iodine. Ideally, iodine supplementation should start 3 months prior to pregnancy. We need future studies evaluating the effect of this strategy.
— Ebru Sulanc, MD