Association between Several Persistent Organic Pollutants and Thyroid Hormone Levels in Cord Blood Serum and Bloodspot of the Newborn Infants of Korea

<div><p>Current knowledge on adverse endocrine disruption effects of persistent organic pollutants (POPs) among newborn infants is limited and often controversial. To investigate the associations between prenatal exposure to major POPs and thyroid hormone levels among newborn infants, both cord serum or maternal serum concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and organochlorine pesticides (OCPs) were compared with five thyroid hormones in cord serum of newborn infants as well as TSH in bloodspot collected at 2 day after birth (n=104). Since cord serum thyroid hormones could be affected by those of mothers, thyroid hormone concentrations of the matching mothers at delivery were adjusted. In cord serum, BDE-47, -99, and Σchlordane (CHD) showed significant positive associations with cord or bloodspot TSH. At the same time, <i>p</i>,<i>p'</i>-dichlorodiphenyldichloroethylene (<i>p</i>,<i>p'</i>-DDE) and hexachlorbenzene (HCB) showed negative associations with total T3 and total T4 in cord serum, respectively. Maternal exposure to <i>β</i>-hexachlorhexane (<i>β</i>-HCH), ΣCHD, ΣDDT, or <i>p</i>,<i>p'</i>-DDE were also associated with neonatal thyroid hormones. Although the sample size is small and the thyroid hormone levels of the subjects were within the reference range, our observation supports thyroid disrupting potential of several POPs among newborn infants, at the levels occurring in the general population. Considering the importance of thyroid hormones during gestation and early life stages, health implication of thyroid hormone effects by low level POPs exposure deserves further follow up investigations.</p></div

Associations between POPs concentrations in maternal blood and thyroid hormone levels in cord blood serum or in bloodspot of newborn infant population in Korea (n = 104).

<p>Signs * and ^ indicate statistical significance of regression parameter at p<0.05, and 0.1, respectively. All POPs concentrations and thyroid hormone levels were natural log—transformed. Results of association regarding free T3, total T3, free T4, total T4, and TSH were adjusted for age, gestation period, mode of delivery, parity, pre-pregnancy BMI, smoking status during pregnancy, and maternal weight gain during pregnancy. While infant sex was added as covariate and smoking status was removed for analysis of bloodspot TSH. Chemicals that were detected > = 75% of the population at concentrations greater than the limit of quantification, a proxy value of ‘limit of quantification divided by square root 2’ was used. For chemicals that were detected in <75% but > = 60%, statistical analysis was conducted with detected values only. Such chemicals are indicated by ‘+’. Since BDE-99 were detected below 60% in maternal serum samples, they were not statistically analyzed.</p><p>Associations between POPs concentrations in maternal blood and thyroid hormone levels in cord blood serum or in bloodspot of newborn infant population in Korea (n = 104).</p

Associations between prenatal POPs concentrations in either maternal or cord blood and thyroid hormone levels of newborn infants.

<p>‘-’ no association;</p><p>‘↑’ positive association;</p><p>‘↓’ negative association (p<0.05);</p><p>Blank cell means data not available. ‘fT3’ free T3; ‘TT3’ total T3; ‘fT4’ free T4; ‘TT4’ total T4. In the present study, cord thyroid hormone levels were adjusted with maternal thyroid hormone levels in the model. Unless otherwise noted, all thyroid hormone measurements were from cord blood or cord serum. ‘s’ indicates the measurement in bloodspot of newborn infant.</p><p>Associations between prenatal POPs concentrations in either maternal or cord blood and thyroid hormone levels of newborn infants.</p

Characteristics of the study population.

<p>^a Normal spontaneous vaginal delivery.</p><p>^b Caesarean section.</p><p>^c Bloodspot TSH was measured from bloodspot samples collected at day 2–7 post-partum. Most newborn babies were collected for bloodspot on day 2 (within 48 hrs) post-partum, but 3 and 2 infants were collected on day 5 and 7 post-partum, respectively.</p><p>Characteristics of the study population.</p

Associations between serum POPs concentrations and thyroid hormones in the sensitivity analysis.

<p>Signs * and ^ indicate statistical significance of regression parameter (β) at p<0.05, and 0.1, respectively. ‘CI’ confidence interval; ‘fT3’ free T3; ‘TT3’ total T3; ‘fT4’ free T4. For the calculation of association, two or more independent variables that were determined as significant predictors to a given thyroid hormone, and at the same time were correlated each other, were added in the multiple regression analysis, in order to identify major predictors. In the regression model, interaction terms between the selected POPs were not included.</p><p>Associations between serum POPs concentrations and thyroid hormones in the sensitivity analysis.</p