Iodine supplementation associated with thyroid dysfunction during first trimester of pregnancy

Iodine intake during the first trimester of pregnancy may lead to maternal thyroid dysfunction in iodine-sufficient or moderately iodine-deficient pregnant women, thus indicating the need to evaluate the iodine nutritional status of this population before recommending iodine supplementation during pregnancy.

“Good iodine nutritional status at the start of and during pregnancy is essential for maintaining proper thyroid function in the mother and encouraging healthy brain development in the fetus and psycho-motor development in the child,” Marisa Rebagliato, PhD, researcher for the Childhood and Environment Project, Spanish Foundation for Science and Technology, said in a press release.

Previous research has suggested a link between increased iodine consumption and hypothyroidism, but data on pregnant woman are limited.

Rebagliato and colleagues assessed the association between iodine nutritional status and thyroid function during the first half of pregnancy (before 24 weeks’ gestation) in 1,844 women from Spain during 2004 to 2008. They examined the consumption of iodine from food, iodized salt, vitamin supplements and ioduria.

Pregnant women who consumed >200 mcg iodine supplements per day were at increased risk for high thyroid-stimulating hormone levels >3 mcgU/mL compared with women who consumed <100 mcg per day (adjusted OR=2.5; 95% CI, 1.2-5.4).

Forty-four percent of women reported consumption of iodized salt; 49% reported taking multivitamins that contained iodine or iodine supplements of at least 100 mcg.

Median ioduria level was 137 mcg/L, which was within the correct limits for the overall population but below the levels recommended by the World Health Organization for pregnancy (150 mcg/L to 249 mcg/L).

The researchers reported no association between urinary iodine and TSH levels.

“Epidemiological monitoring of nutritional iodine status should be carried out on this population before making any automatic recommendations about taking iodine supplements during pregnancy. And above all, people should be encouraged to take iodized salt to ensure they have sufficient iodine levels long before pregnancy,” the researchers concluded.

Rebagliato M. Epidemiology. 2010;21:62-69.