Consequences of Iodine Deficiency in Pregnancy

Iodine is an essential micronutrient for thyroid hormone synthesis. Thyroid hormone is critical for normal fetal development. During the early stages of pregnancy, the fetus depends solely on maternal thyroid hormone crossing the placenta. Therefore, adequate iodine nutrition and normal thyroid function are especially important during pregnancy, as there is an increased demand for iodine in pregnancy. In addition to increased thyroid hormone production, increased urinary iodine losses and transplacental transport of iodine for fetal thyroid hormone synthesis leads to increased iodine requirement in pregnant women. Consequently, the World Health Organization (WHO) recommends higher iodine intake of 250 µg/day in pregnant women, compared to 150 µg/day in non-pregnant adults. Still, iodine deficiency remains a leading cause of maternal hypothyroidism worldwide. Despite global efforts such as salt iodization by Iodine Global Network (IGN) and other organizations, 35 million newborns are estimated to be unprotected from adverse consequences of iodine deficiency worldwide. A recent survey by IGN showed that pregnant women had inadequate iodine status in 23 out of 34 countries assessed. Maternal iodine deficiency in pregnancy has been associated with increased risks of obstetric complications such as miscarriage, prematurity, stillbirth, and low birth weight in offspring. Maternal iodine deficiency has also been associated with impaired neurodevelopment, including cretinism and lower IQ.

Although the adverse effects of severe maternal iodine deficiency are clear, the effects of mild-to-moderate iodine deficiency in pregnancy have been more variable. Some studies showed increased risks of early miscarriage, preterm labor, and low birth weight in offspring, and lower literacy, verbal IQ, reading scores, and fine motor development in children in mild-to-moderate iodine deficiency. On the other hand, some studies reported no significant association between maternal iodine status and verbal skills in child or adverse pregnancy outcomes. There are only a few studies assessing the effect of iodine supplementation during pregnancy on pregnancy or childhood developmental outcomes. Some studies showed higher developmental scores in offspring of women with iodine supplementations, while others did not. The results are limited by the variable exposure time during pregnancy and in some cases, initiation of iodine supplementation later in pregnancy, and lack of significant differences in iodine status of pregnant women between iodine supplementation and non-iodine supplementation groups.

This Research Topic will explore the following topics in the form of Clinical Trial, Original Research, Review, Min-Review, and Systematic Review articles:

-Iodine nutrition in pregnancy
- Iodine supplementation in pregnancy
- Consequences of iodine deficiency in pregnancy
- Iodine nutrition in breastfeeding