Hypothyroxinemia induced by mild iodine deficiency deregulats thyroid proteins during gestation and lactation in dams

What Iodine Intervention Measures Should Be Taken in Different Water Iodine Areas? Evidence from a Cross-sectional Chinese Survey

The aim of this study was to assess the population's iodine nutrition and thyroid diseases in different water iodine areas and to offer suggestions to the governments of different countries to adjust the present policy in different water iodine areas. A cross-sectional survey was conducted in different water iodine areas in China. Urinary iodine, water iodine, salt iodine and thyroid function were determined. The thyroid volumes and nodules were measured by ultrasound. Upon categorization by water iodine level for the 10.0 ~ 39.9 μg/L, 40.0 ~ 100.0 μg/L and 100.1 ~ 150.0 μg/L areas, in adults, the prevalence of subclinical hypothyroidism was 9.28%, 5.35% and 11.07%, and the median urinary iodine (MUI) was 153.7 μg/L, 189.8 μg/L and 317.0 μg/L; in children of the three areas, the prevalence of goitre was 3.83%, 4.47% and 16.02%, and the MUI was 164.1 μg/L, 221.0 μg/L and 323.3 μg/L; in pregnant women of those areas, the MUI was 148.6 μg/L, 176.9 μg/L and 324.9 μg/L. Logistic regression results indicated that low iodine intake was a risk factor for developing hypothyroxinaemia in pregnant women. The iodine status of pregnant women is insufficient in areas with a median water iodine level of 10.0 ~ 39.9 μg/L. Low iodine intake increases the risk of developing hypothyroxinaemia in pregnant women. The iodine status of adults and children is excessive, and the iodine status of pregnant women is above the requirements in areas with a median water iodine concentration of 100.1 ~ 150.0 μg/L. Iodized salt, especially for pregnant women, should be supplied in areas with a median water iodine concentration of 10.0 ~ 39.9 μg/L to improve the iodine status of pregnant women. Supplying non-iodized salt is not enough to protect local residents from the harm from excess iodine in areas with a median water iodine concentration above 100.0 μg/L.

Iodine excess exposure during pregnancy and lactation impairs maternal thyroid function in rats

Adequate maternal iodine consumption during pregnancy and lactation guarantees normal thyroid hormones (TH) production, which is crucial to the development of the fetus. Indeed, iodine deficiency is clearly related to maternal hypothyroidism and deleterious effects in the fetal development. Conversely, the effects of iodine excess (IE) consumption on maternal thyroid function are still controversial. Therefore, this study aimed to investigate the impact of IE exposure during pregnancy and lactation periods on maternal hypothalamus-pituitary-thyroid axis. IE-exposed dams presented reduced serum TH concentration and increased serum thyrotropin (TSH) levels. Moreover, maternal IE exposure increased the hypothalamic expression of Trh and the pituitary expression of Trhr, Dio2, Tsha and Tshb mRNA, while reduced the Gh mRNA content. Additionally, IE-exposed dams presented thyroid morphological alterations, increased thyroid oxidative stress and decreased expression of thyroid genes/proteins involved in TH synthesis, secretion and metabolism. Furthermore, Dio1 mRNA expression and D1 activity were reduced in the liver and the kidney of IE-treated animals. Finally, the mRNA expression of Slc5a5 and Slc26a4 were reduced in the mammary gland of IE-exposed rats. The latter results are in accordance with the reduction of prolactin expression and serum levels in IE-treated dams. In summary, our study indicates that the exposure to IE during pregnancy and lactation induces primary hypothyroidism in rat dams and impairs iodide transfer to the milk.

First trimester isolated maternal hypothyroxinaemia: adverse maternal metabolic profile and impact on the obstetrical outcome

BACKGROUND

Isolated maternal hypothyroxinaemia (IH) is defined as low maternal FT4 (<5th percentile) and normal thyroid-stimulating hormone. There is concern on its potential negative effects on the mother and offspring.

OBJECTIVE

We aimed to evaluate the prevalence of IH and to assess the consequences of hypothyroxinaemia on the maternal and foetal outcomes.

SUBJECTS AND METHODS

From a total of 1300 consecutive pregnant women recruited during the prenatal screen (mean gestational age, 11·8 weeks), thyroid function parameters were assessed in 879 women. After exclusion of women with T4 supplements, with twin pregnancies and with diabetes, data from 783 women were included. Maternal and neonatal outcomes in 55 selected women with IH and negative thyroid auto-antibodies without thyroid disorders or pregnancy achieved through assisted reproductive techniques were compared with a selected euthyroid control group (N = 165).

RESULTS

Among the 783 non diabetic singleton pregnant women, 68 women (8·7%) were identified with IH. When compared to the selected euthyroid controls, selected women with hypothyroxinaemia had significantly increased body mass index (BMI) in preconception (P = 0·003), in the first trimester (P = 0·004) and at the time of delivery (P = 0·001). At term, foetal breech presentation and caesarean section rate were significantly higher (P = 0·006 and P = 0·026, respectively) than in the euthyroid controls. A significant increase in macrosomia was also noted (P = 0·026).

CONCLUSION

The prevalence of hypothyroxinaemia in early pregnancy was of 8·7%. IH is associated with an increased maternal BMI and is related with a risk of breech presentation, a significant increase in macrosomia and caesarean sections. Screening should consider overweight as risk factor for hypothyroxinaemia.