Iodine Status, Thyroid Function, and Birthweight: A Complex Relationship in High-Risk Pregnancies

Effect of Iodine Nutrition Status on Thyroid Function and Pregnancy Outcomes

Iodine is essential for normal thyroid function, supporting healthy fetal and child development. The relevance between maternal iodine nutrition status and pregnancy outcomes remains controversial. The aim was to explore whether urinary iodine concentrations (UIC)/urinary creatinine (UCr) was associated with thyroid function and adverse pregnancy outcomes. This study was performed in the Department of Endocrinology and Metabolism of the First Affiliated Hospital of Nanjing Medical University. A total of 212 pregnant women were enrolled from May 2018 to November 2021, from the first visit until postpartum. Maternal serum samples were obtained in the second half of pregnancy, and then thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), UIC, and UCr were tested. The correlation of UIC/UCr, which represented maternal iodine nutrition status, with TSH, FT4, and FT3 was studied using linear regression. And we assessed associations between UIC/UCr and pregnancy outcomes. Notably, we explored consistency between UIC/UCr and the incidence of low birth weight (LBW) by application of logistic regression analysis. A total of 212 women were divided into 3 groups according to the upper and lower quartiles of UIC/UCr. There were 53 women in group 1 (UIC/UCr < 106.96 ug/g), 106 women in group 2 (UIC/UCr 106.96-259.08 ug/g), and 53 women in group 3 (UIC/UCr > 259.08 ug/g). The level of UIC/UCr had a negative correlation with FT4 (r =  - 0.139, p = 0.043) but a positive correlation with TSH (r = 0.096, p = 0.162 > 0.05). There was a significant difference in the incidence of LBW among the 3 groups (p = 0.007). Logistic regression analysis found that the level of UIC/UCr was an independent factor for LBW (p = 0.048, OR = 0.991, 95%CI (0.982, 0.999)). The receiver operating characteristic (ROC) curve showed that the area under the curve (AUC) for UIC/UCr predicting the incidence of low birth weight was 0.687 (p = 0.013, 95%CI 0.575, 0.799). Lower UIC/UCr during pregnancy was associated with higher FT4 and lower TSH. And iodine deficiency during pregnancy is a risk factor for low birth weight. Our findings indicated that more attention should be paid to the appropriate iodine nutrition status in pregnant women, which can help prevent suffering from adverse pregnancy outcomes.

Association of exposure to ambient particulate matter with maternal thyroid function in early pregnancy

BACKGROUND

It is known that maternal thyroid dysfunction during early pregnancy can cause adverse pregnancy complications and birth outcomes. This study was designed to examine the association between ambient particulate matter with aerodynamic diameters ≤2.5 μm (PM2.5) and particulate matter with aerodynamic diameters ≤10 μm (PM10) exposure and maternal thyroid function during early pregnancy.

METHODS

This study was based on data from a birth cohort study of 921 pregnant women in China. We estimated associations between ambient PM2.5 and PM10 exposure during the first trimester of pregnancy (estimated with land-use regression models) and maternal thyroid hormone concentrations (free thyroxine (FT4), free tri-iodothyronine (FT3), and thyroid-stimulating hormone (TSH)) collected between weeks 10 and 17 of gestation using linear regression models adjusting for potential confounders. Ambient PM2.5 and PM10 concentrations were modeled per interquartile range (IQR) increment and as tertiles based on the distribution of the exposure levels.

RESULTS

An IQR increment (68 μg/m3) in PM2.5 exposure was associated with a significant decrease in maternal FT4 levels (β = -0.60, 95% CI: -1.07, -0.12); and a significant decrease in FT4/FT3 ratio (β = -0.13, 95% CI: -0.25, -0.02). Further analyses showed that, relative to the lowest tertile, women in both the middle and highest tertiles of PM2.5 had significantly lower concentrations of maternal FT4 and FT4/FT3 ratio. No significant associations were found between PM2.5 and FT3 or TSH levels. PM10 exposure was not significantly associated with maternal thyroid function.

CONCLUSIONS

Our study suggested that higher ambient PM2.5, not PM10, exposed during the first trimester of pregnancy were associated with a significant decrease in maternal serum FT4 concentrations and FT4/FT3 ratio. Studies in populations with different exposure levels are needed to replicate our study results.

Potential Risk Factors for Isolated Hypothyroxinemia in Women of Childbearing Age-Results from Retrospective Analysis

Isolated hypothyroxinemia (IH) unfavorably affects reproduction. This study aimed to evaluate retrospectively if any routinely measured clinical/laboratory parameters are associated with IH among women of childbearing age hospitalized in the endocrine department. A group of 466 female non-pregnant inpatients (age range 13-57 years) was considered. IH (decreased free thyroxine (FT4) with normal TSH) was found in 8/466 patients (1.72%). Vitamin D deficiency (<30 ng/mL) was found in all patients with IH, whereas severe Vitamin D deficiency (<20 ng/mL) was found in 5/6. Vitamin D concentration was lower in IH females. FT4 concentration was lower in patients with severe vitamin D deficiency and correlated positively with vitamin D concentration. Insulin resistance index (IRI) was increased (>1.25) in 5/6 patients with IH. IRI was higher in IH patients and it was the only independent linear factor for IH in the univariate regression. FT4 concentration was lower in patients with increased IRI and correlated negatively with IRI. FT4 concentration correlated negatively with body mass index (BMI) and LDL cholesterol or triglycerides, and positively with HDL cholesterol or HDLC/cholesterol ratio. Vitamin D deficiency, insulin resistance and increased BMI (as potential causative factors), and abnormal lipid profile (as a possible consequence), are associated with IH in women of childbearing age. Eliminating risk factors for hypothyroxinemia may improve reproductive health.

The role of placental iodine storage in the neonatal thyroid stimulating hormone surge: iodine as a driving force to adapt the terrestrial life

PURPOSE

Iodine plays a pivotal role in adaptation during the transition from intrauterine to extrauterine life. Although it is well known that the placenta plays a role in iodine storage, a relationship between the neonatal thyroid stimulating hormone (TSH) peak and placental iodine concentration has not been established. This study focuses on the role of placental iodine concentration in the TSH surge after delivery.

MATERIALS AND METHODS

This study included 42 mothers and their newborns, none of whom had perinatal risk factors. The following samples were collected to analyze iodine: placental tissue, amniotic fluid (AF), and 24-h maternal urine. Blood was drawn from the umbilical cord (uc), newborns (at the 1st-24th hours), and mothers (at 1st hour) to analyze the following hormones: TSH, freeT4/T3(fT4/fT3), human chorionic gonadotrophin (hCG), prolactin (PRL), follicle stimulating hormone (FSH), luteinizing hormone (LH), and cortisol.

RESULTS

The mean iodine levels of placental tissue, AF, and 24-h maternal urine were as follows: 29.06 ± 45.88 μg/kg, 182.80 ± 446.51 µg/L, and 498.35 ± 708.34 µg/L, respectively. The mean TSH and hCG values were 32.41 ± 13.96mIU/ml and 30.66 ± 18.55mIU/ml, respectively, at the 1st hour. Placental iodine had strong, very strong, and weak negative correlations with TSH, hCG, and PRL, respectively (r_TSH = - 0.763, p < 0.001;r_HCG = - 0.919, p < 0.001; r_PRL = - 0.312, p = 0.044).

CONCLUSION

This study showed that the placental iodine level was inversely correlated with neonatal TSH, hCG, and PRL. It indicates that placental iodine concentration is an efficient driving force shaping the dynamic pattern of the neonatal TSH peak in addition to hCG and PRL surges, which reflects the adaptive effort in the transition from intrauterine to extrauterine life.

Characterization of Fetal Thyroid Levels at Delivery among Appalachian Infants

Thyroid disorders are a frequently encountered issue during pregnancy and a cause of maternal and fetal morbidity. In regions like Appalachia that are particularly susceptible to health disparities, descriptive studies are needed to assist in identifying pathologic derangements. We sought to characterize fetal thyroid hormone levels at delivery and investigate whether or not maternal demographic characteristics affect the prevalence of neonatal thyroid disease. A cross-sectional analysis was conducted on 130 pregnant women recruited from the Tri-State region, incorporating areas of Kentucky, Ohio, and West Virginia. Total triiodothyronine (T3) (p = 0.4799), free T3 (p = 0.6323), T3 uptake (p = 0.0926), total thyroxine (T4) (p = 0.8316), free T4 (p = 0.0566), and Thyroid stimulating hormone (TSH) (p = 0.8745) levels were comparable between urban and rural newborns. We found no effect of hypertension status or nicotine levels on fetal umbilical cord thyroid hormone levels. Maternal diabetic status was associated with lower T4 (p = 0.0099) and free T4 (p = 0.0025) levels. Cotinine affected levels of T4 (p = 0.0339). In regard to maternal Body Mass Index (BMI), there was an increase in total T3 as BMI increased (p = 0.0367) and no significant difference in free T3, T3 uptake, T4, free T4, or TSH. There was a negative correlation between TSH and 1 min Apgar scores (p = 0.0058). Lead and cadmium have been implicated to alter TSH levels, but no correlation was found in our study (r² = 0.0277). There were no differences in cord blood between urban (37.3 ± 10.3 fmol/ug DNA) and rural (70.5 ± 26.8 fmol/ug DNA) benzo(a)pyrene DNA adducts (p = 0.174). Thyroid disorders present a unique opportunity for the prevention of perinatal morbidity and mortality, since maternal treatment, as well as maternal demographic characteristics, can have direct fetal effects.

Reference Values of Thyroid Hormones During the First Trimester of Pregnancy in Valencian Community (Spain) and Their Relationship with Iodine Intake

Thyroid hormones require special monitoring during the first trimester of gestation. Local reference values should be applied if available, especially in iodine-deficient areas, as generalized iodine supplementation is controversial. The aim of the present study was to establish thyroid stimulating hormone (TSH) and free thyroxine (FT4) reference values in the first trimester of gestation in the Valencian community (Spain) and relate them to iodine intake. A total of 261 healthy pregnant women participated in the study. The calculated reference values were 0.128–4.455 mIU/L for TSH and 0.9–1.592 ng/dL for FT4. The upper TSH reference value for pregnant women in the first trimester in our environment was similar to the latest American Thyroid Association (ATA) recommendation (4 mIU/L). The mean TSH value was significantly lower in smokers, and there were no significant differences when analyzing the influence of iodine supplementation, although the low duration of supplement intake needs to be taken into consideration. Ioduria levels (median 57 µg/L) confirmed iodine deficiency. We found statistically significant differences in ioduria levels among patients who consumed iodized salt and iodine supplements and those who did not. It is essential to focus on recommending adequate consumption of iodized salt and iodine supplements prior to gestation and at least during the first trimester to avoid possible maternal thyroid dysfunction and perinatal complications.