Prenatal (chemical) check-up Study examines environmental chemicals in pregnant women, fetuses and infants in Canada

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Canada’s largest study of environmental chemicals in pregnant women, fetuses and infants is underway. The Maternal-Infant Research on Environmental Chemicals (MIREC) study will measure the extent to which pregnant women, fetuses and infants are exposed to environmental chemicals, as well as tobacco smoke. The study will also assess what pregnancy health risks are associated with exposure to heavy metals, and measure the levels of environmental chemicals as well as some of the beneficial components of breast milk.

The five-year national study is a key deliverable of the Government of Canada’s Chemicals Management Plan, and is in response to the scarcity of reliable data on the levels of environmental chemicals in the bodies of people living in Canada. The MIREC study will fill in the gaps left by the Canadian Health Measures Survey, a two-year study launched early in 2007 under the Chemicals Management Plan, which will provide much needed national data on exposure of the Canadian population to several important contaminants, but will not collect data for pregnant women.

“Infants, pregnant women and fetuses are potentially vulnerable groups,” says Sarah Quelch, research coordinator of the study’s Vancouver site. “We’re hoping to create a profile of pregnant women’s health across Canada that will help contribute to policy decisions with regard to acceptable levels of environmental chemicals.”

We are all exposed to environmental chemicals in many different ways, including through inhalation, skin contact and ingestion. The MIREC study will look at participants’ diets because one of the primary routes of exposure to chemicals is through food and water. Researchers will also look at where participants live, whether in urban or rural areas, to determine differences in airborne exposure, and they will look at workplace exposure to chemicals. Participants will be asked whether they have recently done home renovations while pregnant, what types of general cleaning products they use, what types of plastics and electronics they come in contact with and whether they have any stain resistant furniture because these activities and products are linked with exposure to a number of heavy metals and toxic chemicals that will be measured in the study.

Women will be recruited during the first trimester of pregnancy and followed through the birth and up to eight weeks after birth. Researchers will measure biological markers of exposure to environmental chemicals and tobacco smoke in the mothers’ blood, urine, hair and breast milk, and through umbilical cord blood and the newborns’ first stool known as the meconium. Mothers will also be asked to complete questionnaires throughout their pregnancy and after birth.

The heavy metals lead, mercury, arsenic, manganese and cadmium will be measured during the study. Chemicals such as phthalates and bisphenol A, which are used in plastics and vinyl, as well as the fire retardants polybrominated diphenyl ethers (PBDEs) will also be measured. Other chemicals to be measured include organochlorine pesticides, which no longer are registered for use in Canada but continue to persist in the environment; organophosphate pesticides, used for insect control; polychlorinated biphenyls (PCBs), formerly used as an ingredient in many industrial materials; cotinine, a by-product of smoking; and perfluorinated compounds, which are used in the manufacture of grease and water repellents.

The goal of MIREC is to obtain not only national-level data on maternal and neonatal exposure to environmental contaminants identified by the federal government as priority substances (due to their harmful effects on human health and the environment), but also to determine if heavy metal exposure is related to elevated maternal blood pressure, hypertension, altered sex ratio and fetal growth retardation as some previous studies have indicated.

Another objective of the study is to acquire Canadian data on smoking behaviour and exposure to tobacco smoke, both active and passive, during pregnancy. This data will likely be used by governments and public health officials to develop policies and programs that encourage pregnant women to quit smoking and avoid exposure to second-hand smoke which has been linked with low birth weight and even miscarriage.

The study will also examine the benefits of breastfeeding versus any of the risks, and will measure current levels of select environmental chemicals, nutrients and immunoprotective components in breast milk. This will help identify environmental and maternal dietary and lifestyle factors that correlate with these levels, and will aid in the development of nutrition programs and environmental policies. “We’re hypothesizing that breastfeeding is still very beneficial because it provides important immunoprotective benefits to the child,” says Quelch.

Secondary exploratory objectives of the MIREC study include measuring the transfer of toxins from mother to fetus in a population of pregnant women in Canada, examining the correlation between maternal and fetal “body burdens,” (i.e., the burden or level of chemicals found in the body) and identifying factors that affect the concentration of heavy metals in newborn infants (as measured by cord blood and meconium analyses). Another interest of the study is to look for ways to prevent metal-induced toxicity using antioxidant vitamins, calcium and selenium. The study will also identify potential sources of exposure, as well as predictors of exposure to environmental chemicals.

“I’m hoping the information gathered in this study will transfer to health policy that will improve the health of women and their children,” says Quelch. “To use an example, we can look at the prevalence of data and research in the '70s with regards to lead and how this was followed by policy decisions which were made to reduce the levels of exposure. The same can be seen with regards to bisphenol A [recently in the news] which we will be measuring and can help inform our decisions with regards to harmful chemicals.”

The MIREC study is still in the process of recruiting around 2,000 women from 10 different cities across Canada: Vancouver (BC Children’s and Women’s Hospital), Calgary (Foothills Hospital), Winnipeg (St. Boniface General Hospital), Sudbury (Sudbury General Hospital), Ottawa (Ottawa Hospital-General Campus), Kingston (General Hospital), Hamilton (McMaster University), Toronto (Mount Sinai Hospital), Montreal (CHU Ste-Justine and Jewish Hospital) and Halifax (IWK Health Centre). Women interested in participating must live in one of the research areas and be planning to give birth at one of the hospitals taking part in the study. Participants will be asked to fill out multiple questionnaires and provide blood, urine, hair and breast milk samples. Quelch says that although the project will continue for the next five years and the data and samples will be looked at throughout this time, if high levels of lead, mercury or cadmium are discovered in a participant’s sample, their doctor will be notified immediately. 

The MIREC study is a collaborative initiative among Health Canada scientists, the Sainte-Justine Hospital in Montreal, and clinical researchers from the other participating cities. The Government of Canada will invest $3.9 million in the study, with Health Canada, the Canadian Institutes of Health Research and the Ontario Ministry of the Environment contributing an additional $200,000.

Carolyn Shimmin is the Information Centre Coordinator at the Canadian Women’s Health Network.