Pregnant Women Receiving Insufficient Iodine Supplementation

Diana Swift

August 31, 2015

A Swedish cross-sectional study published online August 20 in Acta Obstetricia et Gynecologica Scandinavica shows that most pregnant women have insufficient iodine intake. The results mirror data from the United States, experts say.

The researchers documented insufficient iodine intake in an analysis of 459 pregnant women.

Led by Michaela Granfors, MD, an obstetrician/gynecologist at University Hospital, Uppsala, Sweden, they found a median urinary iodine concentration of just 98 μg/L (interquartile range, 57 - 148 μg/L) among the women tested, which is considerably below the international recommendation for pregnancy of 150 to 249 μg/L.

"This may have a negative impact on motor and cognitive functions of the offspring," the investigators write. They call for a national assessment of iodine status in pregnant women and cite a need for targeted intervention strategies to optimize gestational intake of this important element. Although nutritional iodine levels are considered adequate in the general Swedish population, the authors note that women require 50% more during pregnancy to maintain maternal and fetal thyroid function.

According to Elizabeth N. Pearce, MD, an endocrinologist at Boston University Medical School in Massachusetts, the median urinary iodine concentration among pregnant US women during 2005 to 2010 was 129 μ/L. "This is consistent with mild iodine deficiency, similar to the situation found in Sweden," she told Medscape Medical News.

The mixed cohort of Swedish mothers to be, aged 18 years and older, all of whom were Swedish-speaking, came from two different counties and from both urban and rural areas and had varying levels of education. Their mean age at delivery date was 31.1 years. The participants underwent third-trimester spot urine sample testing for median urinary iodine concentration. The authors excluded women who smoked or who had diabetes before pregnancy or known thyroid disease before or during pregnancy.

The authors point out that data from other European countries also indicate insufficient iodine intakes in pregnant women, with only a third of European populations having sufficient iodine levels. In addition, recent findings from the United Kingdom suggest that 8-year-olds whose mothers had mild to moderate iodine deficiency early in pregnancy had an increased risk of being in the lowest verbal interquartile quartile. In a 9-year follow-up, mild iodine deficiency during pregnancy also was associated with reduced educational outcomes in the offspring.

The authors call for randomized controlled trials to clarify whether iodine supplementation will benefit pediatric neurodevelopment in countries with mild to moderate iodine deficiency. They note that gestational iodine deficiency can negatively affect infant and maternal thyroid function, with another of their recent studies showing a high prevalence of thyroid disturbances during pregnancy.

Dr Pearce points to expert recommendations from such groups as the American Thyroid Association, Endocrine Society, and European Thyroid Association that women who are pregnant, lactating, or planning to conceive take a daily supplement of 150 μg iodine.

When asked whether the current recommendations on reducing dietary sodium to mitigate hypertension risk play a role in the iodine deficits, Dr Pearce said it is unlikely. "In the US, recommendations for sodium reduction probably have had only a relatively minor effect on dietary iodine intake," said Dr Pearce. "Salt iodization has never been mandated in the US, and currently only 53% of household salt is iodized. The vast majority of salt we ingest in the US is from commercially processed foods, and food processors typically do not use iodized salt."

Similarly, in Sweden, where iodine fortification of edible salt is also voluntary, sales figures from 2012 indicate that only 27% of all salt sold is iodized. In both countries, dairy foods are a very important source of dietary iodine, and in Sweden, fish is also a major iodine source.

This study was supported by grants from the Gillbergska Foundation, Uppsala, Sweden, and grants from the Department of Women's and Children's Health, University Hospital Uppsala, Sweden. The authors have disclosed no relevant financial relationships.

Acta Obstet Gynecol Scand. Published online August 20, 2015. Abstract

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