Effects of Maternal Iodine Status during Pregnancy and Lactation on Maternal Thyroid Function and Offspring Growth and Development: A Prospective Study Protocol for the Ideal Breast Milk Cohort

Selenium levels and their association with thyroid autoimmunity and severe preeclampsia in pregnancy: Insights from a prospective ideal breast milk cohort study

Objective

This study aimed to assess selenium status in South Korean pregnant women and its impact on maternal thyroid function and pregnancy outcomes.

Methods

'Ideal Breast Milk (IBM) Cohort Study' included 367 pregnant women out of 442 participants and categorized into three groups based on plasma selenium levels: deficient (< 70 μg/L), suboptimal (70-99 μg/L), and optimal (≥ 100 μg/L). During the second or third trimester, various blood parameters, including selenium, thyroid-stimulating hormone, free T4, free T3, and anti-thyroid peroxidase antibody levels, were measured. Thyroid parenchymal echogenicity was assessed as another surrogate marker for thyroid autoimmunity using ultrasonography.

Results

The median plasma selenium was 98.8 (range: 46.7-206.4) μg/L, and 30 individuals (8%) were categorized as deficient, while 164 (45%) were classified in the suboptimal group. Selenium deficiency was associated with markers of autoimmune thyroiditis, including positive anti-thyroid peroxidase antibody results (13.3 (deficient) vs 4.6 (optimal) %, P = 0.031) and thyroid parenchymal heterogeneity on ultrasound (33.3 (deficient) vs 14.6 (suboptimal) vs 17.3 (optimal) %, P = 0.042), independently of gestational age. The incidence of severe preeclampsia was higher in the group not taking selenium supplements, particularly among those with twin pregnancies, compared to the group taking selenium supplements (0 (selenium supplement) vs 9.0 (no supplement) %, P = 0.015).

Conclusion

Pregnant women experience mild selenium deficiency, which can lead to significant health issues including maternal thyroid autoimmunity and obstetrical complications during pregnancy. Guidelines for appropriate selenium intake according to the stage of pregnancy and the number of fetuses are needed.

High intakes of iodine among women during pregnancy and the postpartum period has no adverse effect on thyroid function

PURPOSE

Given the high consumption of seaweed soup by pregnant and lactating Korean women, concerns have been raised about excessive iodine intake. We evaluated the effects of maternal iodine intake on maternal thyroid function and birth outcomes. We also evaluated iodine intake via seaweed soup during late pregnancy and the early postpartum period.

METHODS

A total of 349 pregnant women of the Ideal Breast Milk cohort were recruited in late pregnancy, of whom 302 revisited after delivery. Three-day dietary records were assessed at each visit. Blood was collected for thyroid function test. Obstetrical and birth outcomes were obtained.

RESULTS

The median dietary iodine intake was 459 μg/day (interquartile range [IQR] 326.5-647.4 μg/day) during pregnancy. Dietary iodine intake by quartile was not significantly associated with maternal thyroid status, or obstetrical or neonatal outcomes. However, the dietary iodine intake in the early postpartum period was 1759 μg/day (IQR 1026.7-2491.1 μg/day) because of a marked increase in seaweed soup consumption. Of all women, 25.8% consumed seaweed soup more than once over the 3 days of dietary records when pregnant, but the figure rose to 93.4% postpartum. Of postpartum women who consumed seaweed soup daily, the median dietary iodine intakes were 1355, 2394, and 3063 μg/day (soup at one, two, and three-or-four meals).

CONCLUSIONS

In these iodine-replete pregnant women, dietary iodine intake during pregnancy showed no effect on maternal thyroid function or birth outcomes. However, iodine intake in the early postpartum period was markedly increased by the frequency of seaweed soup consumption.

Associations between maternal thyroid function in pregnancy and child neurodevelopmental outcomes at 20 months in the Seychelles Child Development Study, Nutrition Cohort 2 (SCDS NC2)

Maternal thyroid hormones facilitate optimal foetal neurodevelopment; however, the exact role of the thyroid hormones on specific cognitive outcomes is unknown. The present study aimed to investigate associations between maternal thyroid function and neurodevelopmental outcomes in the Seychelles Child Development Study (SCDS) Nutrition 2 cohort (n 1328). Maternal free thyroid hormones (fT3, fT4 and fTSH) were assessed at 28 weeks' gestation with a range of child cognitive outcomes analysed at 20 months. Dietary iodine intake was analysed for a subset of women through a Food Frequency Questionnaire. Linear regression analysis was used to test associations between serum concentrations of maternal thyroid hormones and child neurodevelopment outcomes. Thyroid hormones were analysed as continuous data and categorised as quintiles. 95% of mothers had optimal thyroid function based on fTSH concentrations. Overall, the present study shows that maternal thyroid function is not associated with neurodevelopmental outcomes in this high fish-eating population. However, a positive association, using quintiles for fT3, was reported for the Mental Developmental Index, between Q3 v. Q4 (β 0⋅073; P 0⋅043) and for Q3 v. Q5 (β value 0⋅086; P 0⋅018). To conclude, mothers in our cohort, who largely have optimal thyroid function and iodine intakes, appear able to regulate thyroid function throughout pregnancy to meet neurodevelopmental needs. However, it is possible that minor imbalances of fT3, as indicated from our secondary analysis, may impact offspring neurodevelopment. Further investigation of the relationship between maternal thyroid function and infant neurodevelopment is warranted, particularly in populations with different dietary patterns and thereby iodine intakes.