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BACKGROUND: Toxic metals, such as lead (Pb), cadmium (Cd), arsenic (As), and mercury (Hg), may be associated with a higher risk of gestational hypertension and preeclampsia, whereas manganese (Mn) is an essential metal that may be protective. OBJECTIVES: We estimated the individual, independent, and joint associations of Pb, Cd, As, Hg, and Mn on the risk of developing gestational hypertension and preeclampsia in a cohort of Canadian women. METHODS: Metal concentrations were analyzed in first and third trimester maternal blood (푛=1,560). We measured blood pressure after 20 wk gestation to diagnose gestational hypertension, whereas proteinuria and other complications defined preeclampsia. We estimated individual and independent (adjusted for coexposure) relative risks (RRs) for each doubling of metal concentrations and examined interactions between toxic metals and Mn. We used quantile g-computation to estimate the joint effect of trimester-specific exposures. RESULTS: Each doubling of third trimester Pb (RR = 1.54; 95% CI: 1.06, 2.22) and first trimester blood As (RR = 1.25; 95% CI: 1.01, 1.58) was independently associated with a higher risk of developing preeclampsia. First trimester blood As (RR = 3.40; 95% CI: 1.40, 8.28) and Mn (RR = 0.63; 95% CI: 0.42, 0.94) concentrations were associated with a higher and lower risk, respectively, of developing gestational hypertension. Mn modified the association with As such that the deleterious association with As was stronger at lower concentrations of Mn. First trimester urinary dimethylarsinic acid concentrations were not associated with gestational hypertension (RR = 1.31; 95% CI: 0.60, 2.85) or preeclampsia (RR = 0.92; 95% CI: 0.68, 1.24). We did not observe overall joint effects for blood metals. DISCUSSION: Our results confirm that even low blood Pb concentrations are a risk factor for preeclampsia. Women with higher blood As concentrations combined with lower Mn in early pregnancy were more likely to develop gestational hypertension. These pregnancy complications impact maternal and neonatal health. Understanding the contribution of toxic metals and Mn is of public health importance. [ABSTRACT FROM AUTHOR]

Background: The developing fetus and pregnant woman can be exposed to a variety of environmental chemicals that may adversely affect their health. Moreover, environmental exposure and risk disparities are associated with different social determinants, including socioeconomic status (SES) and demographic indicators. Our aim was to investigate whether and how maternal concentrations of a large panel of persistent and non-persistent environmental chemicals vary according to sociodemographic and lifestyle characteristics in a large pregnancy and birth cohort.Methods: Data were analyzed from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a cohort of pregnant women (N=2001) recruited over four years (2008-2011) in 10 cities across Canada. In all, 1890 urine and 1938 blood samples from the first trimester (1st and 3rd trimester for metals) were analysed and six sociodemographic and lifestyle indicators were assessed: maternal age, household income, parity, smoking status, country of birth and pre-pregnancy body mass index (BMI).Results: We found these indicators to be significantly associated with many of the chemicals measured in maternal blood and urine. Women born outside Canada had significantly higher concentrations of di-2-ethylhexyl and diethyl phthalate metabolites, higher levels of all metals except cadmium (Cd), as well as higher levels of polychlorinated biphenyls (PCBs) and legacy organochlorine pesticides (OCPs). Nulliparity was associated with higher concentrations of dialkyl phosphates (DAPs), arsenic, dimethylarsinic acid (DMAA), perfluoroalkyl substances (PFASs) and many of the persistent organic pollutants. Smokers had higher levels of bisphenol A, Cd and perfluorohexane sulfonate, while those women who had never smoked had higher levels of triclosan, DMAA, manganese and some OCPs.Conclusion: Our results demonstrated that inequitable distribution of exposure to chemicals among populations within a country can occur. Sociodemographic and lifestyle factors are an important component of a thorough risk assessment as they can impact the degree of exposure and may modify the individual's susceptibility to potential health effects due to differences in lifestyle, cultural diets, and aging. [ABSTRACT FROM AUTHOR]

Epidemiological studies have hypothesized that both insufficient and excess blood manganese (Mn) levels during pregnancy are associated with reduced fetal growth. This literature is characterized by inconsistent results and a limited focus on women with exposures representative of the general North American population. We examined the relationship between maternal and cord blood Mn levels and fetal growth among women enrolled in the Maternal-Infant Research on Environmental Chemicals Study (MIREC). Mothers with singleton, term infants and complete maternal first and third trimester blood Mn data were eligible for inclusion in the present study (n = 1519). Mean birth weight and odds ratios of small for gestational age (SGA) births according to maternal and cord blood Mn levels (low (<10), referent (10-<90), high (≥90) percentiles) were estimated. We also evaluated the association between the ratio of cord and maternal blood Mn and birth weight. Women with low (<0.82 μg/dL) maternal blood third trimester Mn levels had infants that weighed an average of 64.7 g (95% CI: -142.3,12.8) less than infants born to women in the referent exposure group. This association was strengthened and became statistically significant when adjusted for toxic metals (lead, mercury, arsenic, and cadmium) [-83.3 g (95% CI: -162.4, -4.1)]. No statistically significant associations were observed in models of maternal first trimester or cord blood Mn. A one unit increase in the cord/maternal blood Mn ratio was associated with a 29.4 g (95% CI: -50.2, -8.7), when adjusted for maternal and neonatal characteristics. Our findings motivate additional research regarding the relation between Mn exposure and fetal growth. Further inquiry is necessary to determine whether an exposure threshold exists, how growth related effects of maternal and fetal Mn may differ, and how concurrent exposure to other toxic metals may impact the association between Mn and growth. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl substances (PFAS) are ubiquitous, persistent chemicals that have been widely used in the production of common household and consumer goods for their nonflammable, lipophobic, and hydrophobic properties. Inverse associations between maternal or umbilical cord blood concentrations of perfluorooctanoic acid and perfluorooctanesulfonate and birth weight have been identified. This literature has primarily examined each PFAS individually without consideration of the potential influence of correlated exposures. Further, the association between PFAS exposures and indicators of metabolic function (i.e., leptin and adiponectin) has received limited attention. We examined associations between first-trimester maternal plasma PFAS concentrations and birth weight and cord blood concentrations of leptin and adiponectin using data on 1,705 mother-infant pairs from the Maternal Infant Research on Environmental Chemicals (MIREC) Study, a trans-Canada birth cohort study that recruited women between 2008 and 2011. Bayesian hierarchical models were used to quantify associations and calculate credible intervals. Maternal perfluorooctanoic acid concentrations were inversely associated with birth weight z score, though the null value was included in all credible intervals (log10 β = -0.10, 95% credible interval: -0.34, 0.13). All associations between maternal PFAS concentrations and cord blood adipocy-tokine concentrations were of small magnitude and centered around the null value. Follow-up in a cohort of children is required to determine how the observed associations manifest in childhood. [ABSTRACT FROM AUTHOR]

Previous evidence suggests that exposure to outdoor air pollution during pregnancy could alter fetal metabolic function, which could increase the risk of obesity in childhood. However, to our knowledge, no epidemiologic study has investigated the association between prenatal exposure to air pollution and indicators of fetal metabolic function. We investigated the association between maternal exposure to nitrogen dioxide and fine particulate matter (aerodynamic diameter ≤2.5 urn) and umbilical cord blood leptin and adiponectin levels with mixed-effects linear regression models among 1,257 mother-infant pairs from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, conducted in Canada (2008-2011). We observed that an interquartile-range increase in average exposure to fine particulate matter (3.2 µg/m³) during pregnancy was associated with an 11% (95% confidence interval: 4, 17) increase in adiponectin levels. We also observed 13% (95% confidence interval: 6, 20) higher adiponectin levels per interquartile-range increase in average exposure to nitrogen dioxide (13.6 parts per billion) during pregnancy. Significant associations were seen between air pollution markers and cord blood leptin levels in models that adjusted for birth weight z score but not in models that did not adjust for birth weight z score. The roles of prenatal exposure to air pollution and fetal metabolic function in the potential development of childhood obesity should be further explored. [ABSTRACT FROM AUTHOR]

Background: Bisphenol A (BPA) and triclosan (TCS) are two nonpersistent chemicals that have been frequently measured in spot urine samples from the general population but less so in pregnant women; however, data are limited on the free (bioactive) and conjugated forms of these phenols. Objectives: The Maternal-Infant Research on Environmental Chemicals (MIREC) Study addressed these data gaps by utilizing stored maternal urine samples from a large multicenter cohort study of Canadian pregnant women. Methods: Concentrations of free and conjugated forms of BPA and TCS were measured in about 1,890 first-trimester urine samples by ultra performance liquid chromatograpy-tandem mass spectrometry using isotope dilution. Results: The glucuronides of BPA and TCS were the predominant forms of these chemicals measured (detected in 95% and 99% of samples, respectively), whereas the free forms were detected in 43% and 80% of samples, respectively. The geometric mean urinary concentrations for glucuronides of BPA and TCS were 0.80 μg/L (95% CI: 0.75, 0.85) and 12.30 μg/L (95% CI: 11.08, 13.65), respectively. Significant predictors of BPA included maternal age < 25 vs. ≥ 35 years, current smoking, low vs. high household income, and low vs. high education. For TCS, urinary concentrations were significantly higher in women ≥ 25 years of age, never vs. current smokers, and women with high household income and high education. Conclusions: The results from this study represent the largest national-level data on urinary concentrations of free and conjugated forms of BPA and TCS in pregnant women and suggest that maternal characteristics predicting elevated urinary concentrations of these phenols largely act in opposite directions. Citation: Arbuckle TE, Marro L, Davis K, Fisher M, Ayotte P, Bélanger P, Dumas P, LeBlanc A, Bérubé R, Gaudreau É, Provencher G, Faustman EM, Vigoren E, Ettinger AS, Dellarco M, MacPherson S, Fraser WD. 2015. Exposure to free and conjugated forms of bisphenol A and triclosan among pregnant women in the MIREC cohort. Environ Health Perspect 123:277-284; http://dx.doi.org/10.1289/ehp.1408187 [ABSTRACT FROM AUTHOR]

Biomonitoring is used increasingly as an indicator and quantitative measure of exposure; however, there is a large gap in interpreting and communicating biomonitoring results to study participants. Two separate, national biomonitoring initiatives are under way in Canada; the household recruitment-based Canadian Health Measures Survey (CHMS) and the clinic recruitment-based Maternal-Infant Research on Environmental Chemicals (MIREC) Study. The CHMS provides participants with the option to receive all their results, but this option is not provided to MIREC participants. The approach to reporting results to participants depends on the availability of reference ranges and guidelines for which tissue concentrations may be interpreted as being elevated or associated with increased health risks, how participants are recruited, unique vulnerabilities of the population, legislation governing access to personal information, and decisions of research ethics committees. It is the researchers' responsibility to present the best case for their approach and, once the decision has been made, to inform participants about access to their results through the consent process. [ABSTRACT FROM AUTHOR]