Iodineminho Study: Iodine Supplementation and Prevalence of Iodine Deficiency In Pregnant Women

Iodine is necessary for proper brain development. The prevalence of iodine deficiency in Portuguese pregnant women led the health authorities, in 2013, to recommend iodine supplementation for women in preconception, throughout pregnancy, and during lactation.

This work aimed to assess the effect of iodine supplementation initiated in the preconception or the first trimester of pregnancy on the prevalence of iodine deficiency and maternal thyroid status.

An observational prospective cohort study was conducted that followed the thyroid function and iodine status of women recruited during preconception or in the first trimester of pregnancy.

Median urinary iodine concentration (UIC) was significantly higher among women taking iodine supplements (no-supplement group UIC = 63 µg/L; supplement group UIC = 100 µg/L; P = .002) but still below the levels recommended by the World Health Organization. Only 15% of pregnant women had adequate iodine status and 17% showed a UIC of less than 50 µg/L. There was no influence whether iodine supplementation was started during preconception or during the first trimester of gestation (UIC preconception group: 112 µg/L vs UIC pregnancy group: 91 µg/L; P = .569). In the first trimester of pregnancy, total thyroxine levels were lower and free triiodothyronine levels were higher in nonsupplemented women. Thyroglobulin levels were lower in women who started iodine supplementation during preconception compared to nonsupplemented women and women who started iodine supplementation during gestation.

In the Minho region of Portugal, fertile women have insufficient iodine intake. Additional public health measures are needed since the current recommendations for iodine supplementation for pregnancy are unsatisfactory to achieve adequate iodine status.