Exploration of the optimal range of urinary iodine concentration in Chinese pregnant women in mildly iodine-deficient and -sufficient areas.

PURPOSE: There is some uncertainty about the optimal ranges for urinary iodine concentration (UIC) during pregnancy. This study aimed to explore associations between maternal UIC and thyroid function in iodine sufficient and mildly iodine deficient areas. METHODS: It was a cross-sectional study in which 1461 healthy pregnant women were enrolled to collect their blood and urine samples during their routine antenatal care in Tianjin and Wuqiang, China. Wuqiang was a mildly iodine-deficient region, while Tianjin was iodine sufficient. UIC, free triiodothyronine (FT3), free thyroid hormone (FT4), thyroid stimulating hormone (TSH), thyroid peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), serum iodine concentration (SIC) including total serum iodine concentration (tSIC) and non-protein bound serum iodine concentration (nbSIC) were assessed during the routine antenatal care visits. RESULTS: The median UIC in pregnant women was 174 (113, 249) µg/L in Tianjin and 111 (63, 167) µg/L in Wuqiang, respectively. Compared with Tianjin, UIC, FT3 and TSH were lower, and FT4, tSIC, nbSIC, rates of TPOAb and TgAb positivity and the thyroid dysfunction rate (TDR) were higher in Wuqiang (P < 0.001). FT3, FT4, tSIC and nbSIC increased during pregnancy in Tianjin with increasing UIC, while only FT3 and nbSIC increased in Wuqiang (P < 0.05). In Tianjin, the TDR increased with UIC and peaked at UIC ≥ 500 µg/L (P = 0.002), while in Wuqiang, the TDR showed a weak "U-shaped" relationship with UIC and the rate was lowest with UIC 100-149 µg/L. CONCLUSIONS: In iodine-deficient areas, there was a lower TDR in pregnant women with UIC 100-149 µg/L. We suspected that the optimal UIC criteria recommended by WHO may be a little high for pregnant women in mild-to-moderate iodine-deficient countries.

Variation of iodine concentration in breast milk and urine in exclusively breastfeeding women and their infants during the first 24 wk after childbirth.

OBJECTIVE: The aim of this study was to observe the variation of iodine concentration in breast milk and urine in exclusively breastfeeding women and their infants during the first 24 wk after childbirth. METHODS: In all, 634 exclusively breastfeeding mother-infant pairs were enrolled at hospital and followed at the 1, 4, 8, 12, 16, and 24 wk postpartum. Spot infant urinary iodine concentration (I-UIC), maternal urinary iodine concentration UIC (M-UIC), and breast milk iodine concentration (BMIC) in bilateral breasts were measured. RESULTS: During the first 24 wk, the median I-UIC was 216 (139-362) and 122 (68-217) µg/L in lactating mothers, both indicating iodine sufficiency. A strong correlation and no difference were found between BMIC in bilateral breasts. The mean BMIC (M-BMIC) of the two breasts was 165 (112-257) µg/L with a Bland-Altman index of 2.1%. Positive correlations were found between M-BMIC and I-UIC (r = 0.353, P < 0.001), between M-BMIC and M-UIC (r = 0.339, P < 0.001), and between I-UIC and M-UIC (r = 0.222, P < 0.001). M-BMIC was significantly higher than M-UIC (P < 0.001) and lower than I-UIC (P < 0.001). M-BMIC declined from week 1 to week 8 postpartum, both I-UIC and M-UIC dropped from week 1 to week 4 postpartum and stabilized thereafter. CONCLUSION: The iodine nutrition in lactating women and infants were adequate during the first 24 wk after childbirth. M-BMIC declined from week 1 to week 8 postpartum. Both I-UIC and M-UIC dropped from week 1 to week 4 postpartum. Further studies are needed to explore a more definitive BMIC and UIC range for an optimal iodine status in lactating women and breastfed infants.

Excessive iodine intake is associated with formation of thyroid nodules in pregnant Chinese women.

In recent decades, the prevalence of thyroid nodules (TNs) has steadily increased in pregnant women. Therefore, this study aimed to investigate associations between TNs and iodine intake in pregnant women. From March 2016 to May 2017, serum and spot urine samples, as well as demographic data and medical history, were collected from 2353 pregnant women. Urine iodine concentration (UIC) and creatinine (Cr) level were determined in spot urine samples; serum thyroid hormones and thyroid autoantibodies were also determined. We examined the hypothesis that excess iodine intake influences incidence of TNs. Herein, TNs were diagnosed by ultrasonography, whereas demographic data and medical history were collected by questionnaire. Multivariate logistic regression models were used to calculate the odds ratios and their corresponding confidence intervals for TN risk factors. Generalized linear mixed model was used to assess the random effects of the regions. The UIC and UIC to creatinine ratio (I/Cr ratio) were significantly higher in pregnant women with TNs (168 and 190 µg/L, respectively, for UIC [P < .01]; 139 and 155 µg/g, respectively, for I/Cr ratio [P < .01]). Thyroglobulin, age, pre-pregnancy body mass index, and iodine-excessive region were associated with TNs (odds ratio = 1.01, 1.06, 1.04, and 2.38, respectively). Whereas I/Cr ratio was not a significant risk factor for TNs in pregnant women when adjusted for potential confounders, iodine excess (I/Cr ratio >500 µg/g) was a risk factor in pregnant women in their second trimester. People living in areas with excessive iodine in drinking water should decrease their iodine intake, and a safe water source should be provided to ensure that the I/Cr ratio of pregnant women can be maintained at an optimal level.

Iodine Nutrition and Thyroid Function in Pregnant Women Exposed to Different Iodine Sources.

Pregnant women are more vulnerable to iodine deficiency and iodine excess. The study aimed to assess the changes in iodine nutrition and thyroid function of pregnant women exposed to different iodine sources resulting in various iodine intakes during pregnancy. From 2016 to 2017, 2004 healthy pregnant women aged 20-35 years from Shandong and Tianjin, China, were enrolled. Urinary iodine concentration (UIC), drinking water iodine content (WIC), thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroid hormone (FT4), thyroglobulin (Tg), serum thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TgAb) were measured. Pregnant women in both Shandong and Tianjin were iodine sufficient, but the median UIC in pregnant women was significantly higher in Shandong (244 µg/L) than that in Tianjin (159 µg/L). No differences were found in UIC over the course of gestation in Shandong. In Tianjin, the UIC decreased during 13-24 weeks and stabilized thereafter. Compared with Tianjin, TSH levels were higher and FT3 and FT4 levels were lower in Shandong. Both FT3 and FT4 significantly decreased during pregnancy in Shandong and Tianjin. TSH and Tg increased over the course of gestation in both Shandong and Tianjin. The iodine status of pregnant women in Tianjin and Shandong were sufficient, but different changing patterns in UIC and thyroid function during pregnancy were presented. More attention should be focused on iodine nutrition of pregnant women, even in iodine-sufficient areas.

[The iodine status of lactating women and the influence on infants in Tianjin City].

OBJECTIVE: To investigate the iodine status of lactating women and the influence on infants during the first 24 weeks postpartum in Tianjin City. METHODS: The iodine concentration of human milk and urine were measured from 438 lactating women and their exclusive breastfeeding infants. RESULTS: Significant difference was found between the levels of BMIC according to the time of collecting samples( P < 0. 001). The BMIC was lower at the 24th week postpartum with a M( P25-P75) of 123. 5 µg/L( 83. 1-177. 6 µg/L) and the level of lactating women's UIC was lower at the 4th week postpartum with the M( P25-P75) of 87 µg/L( 52-159 µg/L). Besides that, the level of infants ' UIC was lower at the 12th week postpartum with the M( P25-P75) of 191 µg/L( 130-302 µg/L). Lactating women's BMIC and UIC( r = 0. 238, P <0. 001), lactating women's BMIC and infants' UIC( r = 0. 257, P < 0. 001), lactating women's UIC and infants' UIC( r = 0. 148, P < 0. 001) were significantly positive correlated. According to different time of collecting samples, the levels of infants' UIC were significant different categorized by BMIC at 4th, 12th, 24th week postpartum( P <0. 05). CONCLUSION: The BMIC gradually decreased during the first 24 weeks postpartum in Tianjin, but still been in the sufficient iodine status. The iodine status of lactating women can affect their infants' iodine status.

Effect of maternal and neonatal factors on neonatal thyroid stimulating hormone: Results from a population-based prospective cohort study in China.

OBJECTIVE: Neonatal TSH screening is effective in detecting congenital hypothyroidism and estimating iodine status in a given population, but various factors influence TSH levels. The aim of this study was to evaluate the effect of maternal and neonatal factors on neonatal TSH levels. DESIGN AND SETTING: Data were obtained from an ongoing prospective cohort study. A total of 988 pregnant women and their newborn infants participated in the study from April 2015 to May 2017 at Tianjin Maternal and Child Health Center and Tanggu Maternity Hospital in Tianjin, China. Maternal demographic information, including age, height, and parity, was recorded by questionnaire. Fasting blood and urinary samples were collected from all pregnant women. After parturition, information on gestation duration, mode of delivery, neonatal sex, neonatal TSH, neonatal birth weight, and neonatal birth height were recorded. RESULTS: Maternal age, maternal BMI, gestation duration, parity, and neonatal birth weight and height were significantly correlated with neonatal TSH (p < 0.05). Quantile regression revealed that maternal age, TSH, FT4, and gestation duration were positively correlated with neonatal TSH level. A logistic regression model identified maternal BMI, TSH, and birth height as risk factors for having neonatal TSH > 5 mIU/L (p < 0.05). CONCLUSION: Neonatal TSH levels are dynamic and may be affected by several maternal and neonatal factors including maternal age, TSH, FT4, and birth weight and height. Identification of these confounders is useful for assessing the status of neonatal thyroid development. STRENGTHS AND LIMITATIONS OF THIS STUDY: (1) Iodine deficiency disorder has generally been eliminated, so the median urinary iodine concentration of pregnancy is higher than 150 µg/L even in mildly or moderately iodine deficient areas. (2) Unlike many other studies, which did not consider the complexity of factors or examined only one or two variables, this study used a multivariate model to analyze the data. (3) This study examined numerous high-risk factors in pregnant women and considered the biological interrelation between them. Future studies should consider these confounding factors for neonatal TSH levels and establish a proper neonatal TSH range for monitoring the iodine status of a population or diagnosing congenital hypothyroidism.