The researchers published their findings in the June 2011 issue of Clinical Endocrinology in an article called “Maternal thyroid function in different conditions of iodine nutrition in pregnant women exposed to mild-moderate iodine deficiency: an observational study.”
The observational cohort included a total of 433 anti-thyroid peroxidase antibody (anti-TPOAb)-negative women:
Maternal thyroid-stimulating hormone (TSH), free T3, and free T4 levels were measured throughout pregnancy. Urinary iodine excretion (UIE) was also gathered from sporadic samples.
There wasn’t a difference in age and parity between the 3 groups. However, researchers found that a comparison of the 3 groups showed that the prevalence of raised TSH levels throughout pregnancy was somewhat higher in the 150-I group than in the I-salt group (p=0.048; odds ratio, 1.97; 95% CI; 1.05 to 3.72), but not different in the no-I group (p=0.51).
In addition, the prevalence of raised TSH and decreased free T4 were: 44 of 168 (26.2%) of the 150-I group, 16 of 105 (15.2%) of the I-salt group, and 47 of 160 (29.4%) of the no-I group. It was also noted that TSH values exceeded the trimester-specific upper limit.
The overall prevalence of decreased free T4 during pregnancy was 8.3% in the 150-I group, 9.5% in the I-salt group, and 20% in the no-I group.
The study also determined that median UIE was higher in the 150-I group than in the I-salt group (p<0.001) or no-I group (p<0.0001), and consistent with a more adequate—although still insufficient—dietary iodine intake for pregnancy (estimated iodine intake was 200 μg per day). UIE considerably increased from the early first trimester (67.2 μg/L) to the late third trimester, (133.7 μg/L); however, this was only observed in the 150-I group (p<0.001).
The study concluded that using iodine-containing supplements regularly was effective in decreasing the risk of inappropriately low free T4 levels in pregnancy. The increased TSH seen in the 150-I group may have been due to a transient stunning effect on the thyroid gland, which occurred as a result of the sudden increase in daily iodine intake.
The importance of gestational iodine supplementation is undisputed, and researchers concluded that in mild to moderately iodine-deficient regions, women who want to conceive should consider taking iodine supplementation several months before pregnancy.