Maternal-Infant Research on Environmental Chemicals (MIREC): published study findings

The MIREC Research Platform will:

  • identify possible risks to maternal and child health
  • produce new knowledge on Canadians' exposure to environmental chemicals

Some summaries of peer-reviewed findings are posted here.

On this page

Description of the MIREC Research Patform

Cohort Profile: the MIREC Research Platform

The MIREC Study was established to obtain national biomonitoring data for pregnant women and their infants. It also examined possible adverse health effects of prenatal exposure to environmental chemicals on pregnancy and infant health.

For information on the study method, visit MIREC Study and Research Platform.

Compared to national averages, women in the MIREC study tended to:

  • be older
  • smoke less
  • have a higher education level

The MIREC study assessed fewer people than many global studies. Still, it has one of the broadest datasets.

The MIREC research platform will be a major resource in the field of prenatal exposure to environmental chemicals. This is due to the:

  • follow-up studies
  • samples collected
  • large amount of data collected

Health Canada will use these results to support risk assessments and risk management of environmental chemicals. There will be a large focus on exposures during pregnancy.

Results of this research are published in the journal Paediatric and Perinatal Epidemiology (2013 Jul;27(4):415-25).

Biomonitoring for environmental chemicals

Chemicals measured in urine during pregnancy

Phthalate and bisphenol A Exposure among pregnant women in Canada

Bisphenol A (BPA) and phthalates are 2 groups of chemicals often measured in urine in population surveys. Data for pregnant women in Canada, however, are limited.

These chemicals were measured in first trimester urine samples from about 2,000 women in the MIREC study. Around 90% of the women had detectable levels of BPA.

An assessment of urine concentrations of BPA by maternal features showed that concentrations:

  • decreased with higher maternal age
  • were higher in current smokers or women who quit during pregnancy
  • tended to be higher in women who:
    • were born in Canada
    • gave a fasting urine sample
    • had lower incomes and levels of education

Some phthalates were found in maternal urine most of the time and others were rarely found. This study provides the first biomonitoring results for a large number of pregnant women sampled in the first trimester of pregnancy.

The results show some parallels to the Canadian Health Measures Survey (CHMS). Levels of exposure to these chemicals in mothers from the MIREC study are close to those found in women in the CHMS. In some cases, they were even lower than the levels found in the CHMS.

These results on levels of exposure will help support risk assessment and risk management activities for these chemicals.

This research is published in the journal Environment International (2014 Jul 68:55-65).

Exposure to free and conjugated forms of bisphenol A (BPA) and triclosan among pregnant women in the MIREC cohort

Triclosan and BPA are 2 chemicals for which data on levels in pregnant women are scarce.

Triclosan is used as an antimicrobial in a wide range of cosmetics and personal care products. This includes non-prescription drugs.

BPA is used to make a hard, clear plastic and may also be found in:

  • thermal papers such as:
    • tickets
    • receipts
  • epoxy resin linings on the inside of metal-based food and drink cans

These chemicals were measured in first trimester urine samples from about 1,900 women in the MIREC study. BPA levels were higher in women who:

  • smoked
  • were under 25 years of age
  • had a lower household income

Triclosan levels tended to be higher in women:

  • who had never smoked
  • were 25 years of age or older

Health Canada will use these results to estimate exposure to these chemicals for Canadians.

The results of this study are published in the journal Environmental Health Perspectives, (2015 Apr;123(4):277-84).

Determinants of urinary concentrations of dialkyl phosphates among pregnant women in Canada: results from the MIREC study

Organophosphates (OPs) are a group of closely related pesticides. They are used in agricultural and non-agricultural sites. These pesticides can affect how the nervous system functions.

High exposure to OPs during pregnancy has been linked to:

  • adverse birth outcomes and
  • poorer neurodevelopment in children

Many of these pesticides have been discontinued or their use has been restricted.

The goal of this study was to examine links between:

  • levels of OP pesticide metabolites in maternal urine and
  • various factors that influence these levels

Six breakdown products of OPs were measured in first trimester urine samples of 1,884 pregnant women. Many factors showed strong links to higher urinary concentrations, such as:

  • being a non-smoker
  • having a higher education
  • fasting prior to urine collection
  • having a normal pre-pregnancy BMI
  • giving a urine sample in the winter season
  • giving a urine sample early or late in the day

Higher urinary concentrations were also linked to first-time pregnancies.

Higher levels of OP pesticides were linked to higher intake of some foods. These include:

  • tomatoes
  • citrus fruits
  • sweet peppers
  • whole grain bread
  • beans and dry peas

The same link to higher concentrations was also found in women who consumed more of some drinks, such as:

  • white wine
  • apple juice
  • green and herbal tea
  • soy and rice beverages

These results may be useful to Health Canada's Pest Management Regulatory Agency. They can be used in the agency's ongoing risk assessment and management of these pesticides.

This study was led by scientists from the University of Montreal. It was published in the journal Environment International (2016 Sep;94:133-140).

Arsenic levels among pregnant women and newborns in Canada: results from the MIREC cohort

Arsenic is a common environmental chemical. It can be found at very low levels in:

  • rice
  • fish and shellfish

Long-term exposure over many years to elevated levels of arsenic can:

  • affect a number of organs
  • contribute to the risk of certain cancers

Of most concern, in terms of health effects in children, is the timing of the exposure. This is because exposures during the prenatal and early-life periods are more prone to be linked to adverse effects.

Arsenic was measured in:

  • umbilical cord blood
  • the baby's first stool
  • first trimester maternal urine
  • first and third trimester maternal blood

About 90% of pregnant women had low, measurable levels of arsenic in their blood. Arsenic was less often detected in umbilical cord blood and the baby's first stool.

Most forms of arsenic that can be measured in urine were rarely found. The only exception was dimethylarsinic acid (DMA).

In this study, arsenic levels in maternal blood and urine were lower than national averages for Canadian women of reproductive age. In general, higher arsenic levels were found in women who:

  • were older
  • had higher education
  • were born outside Canada

More research is needed to find factors that may influence arsenic exposure in pregnant women and infants. Future research should also assess possible health effects, if any.

Health Canada will use the results of this study to support risk assessments and risk management of arsenic.

This study was done with scientists from:

  • the Yale School of Public Health
  • the Institut national de santé publique du Québec
  • Sainte-Justine University Hospital Research Centre, University of Montreal

This work was published in the journal Environmental Research (2017 Feb;153:8-16).

Chemicals measured in blood during pregnancy, umbilical cord blood and baby's first stool

Maternal and fetal exposure to cadmium, lead, manganese and mercury: the MIREC study

Canadian data are scare on levels of possible harmful environmental metals in:

  • pregnant women
  • developing fetuses

Using the MIREC study, 4 metals were measured in first and third trimester maternal blood samples, as well as:

  • baby's first stool
  • umbilical cord blood

The metals measured were:

  • lead
  • mercury
  • cadmium
  • manganese

Information about foods eaten and dietary supplements taken was also used to assess nutrient intake of:

  • iron
  • calcium
  • vitamin D

Trace amounts of 3 metals were found in maternal blood:

  • lead
  • mercury
  • cadmium

Of those metals, cadmium was rarely found in cord blood or the baby's first stool. For lead and mercury, average levels were higher in cord blood compared to maternal blood.

Manganese was found in all the biospecimens tested. Manganese is an essential nutrient that is needed for human health, even more so in pregnancy.

Higher calcium intake was linked to lower third trimester levels of maternal:

  • lead
  • mercury
  • cadmium
  • manganese

Higher calcium intake was also linked to lower levels of lead in cord blood.

Higher intake of vitamin D was linked to lower third trimester levels of maternal blood:

  • lead
  • cadmium
  • manganese

Vitamin D intake was also linked to lower levels of cord blood lead.

These results showed that the transfer of metals between maternal and cord blood differed by metal. There was much less transfer of cadmium from mother to fetus.

Getting more dietary calcium and vitamin D during pregnancy may also be linked to lower levels of:

  • maternal lead
  • cord blood lead
  • maternal cadmium

These results can help support Health Canada's risk management of metals in pregnancy. They can also support advice on good nutrition in pregnancy.

This study was published in the journal Chemosphere (2016 Nov;163:270-282).

Concentrations of persistent organic pollutants in maternal and cord blood from the MIREC cohort study

Persistent organic pollutants (POPs) are chemicals that linger in the environment. These chemicals build up in fatty tissues of humans and animals. There may be a link between higher exposure to some of these chemicals and certain health effects, such as:

  • cancer
  • birth defects.

Assessing environmental exposures in pregnant women is vital, given how vulnerable the developing fetus is. This study measured several POP levels in first trimester maternal blood and umbilical cord blood samples.

The study showed women were exposed to several chemicals. Many of these chemicals were banned from use in Canada years ago.

However, compared to other studies, those who took part in the MIREC study had lower chemical levels in their blood.

Many factors impacted chemical levels, including:

  • income
  • education
  • maternal age
  • smoking status
  • pre-pregnancy BMI
  • number of previous pregnancies
  • place of birth (if born outside Canada)

The results of this study will help to:

  • support risk assessment and risk management activities by Health Canada
  • develop public health measures to protect pregnant women from the effects of environmental chemical exposure

This work was published in the journal Environmental Health (2016 May 4;15(1):59).

Nutritional status

Total folate and unmetabolized folic acid in the breast milk of a cross-section of Canadian women

Folate needs increase during pregnancy and lactation. A supplement with folic acid is advised for women who:

  • are lactating
  • are pregnant
  • could become pregnant

The goals of this study were to:

  • measure total folate and unmetabolized folic acid (UMFA) content in breast milk and
  • assess the relationship of breast milk folate and folic acid with folic acid supplement use in Canadian mothers

Breast milk levels of several forms of folic acid were measured using specialized techniques and equipment. The forms measured included:

  • UMFA
  • tetrahydrofolate (THF)
  • 5-formylTHF
  • 5-methylTHF
  • 5,10-methenylTHF

Total daily intake of folic acid was based on self-reported supplement use.

The study found that UMFA was detectable in the milk of 96.1% of the women.

Total daily folic acid supplement intake was linked to breast milk folate levels and forms. Breast milk total folate was 18% higher in supplement users than non-users. Women consuming more than 400 micrograms of folic acid per day drove this difference.

UMFA was 126% higher and 5-methylTHF 19% lower in supplement users than non-users. Women consuming more than 400 micrograms of folic acid per day had lower 5-methylTHF and higher UMFA. This is when compared to women consuming 400 or fewer micrograms per day.

This study showed that folic acid supplement use was linked to modestly higher breast milk total folate. It also showed that detectable breast milk UMFA was found in nearly all participants.

Breast milk UMFA was proportionally higher than 5-methylTHF in women who consumed more than 400 micrograms of folic acid per day. This suggests that higher folic acid supplement doses exceed the body's ability to metabolize folic acid. This can then lead to more UMFA in breast milk.

For this reason, taking folic acid supplement doses higher than 400 micrograms may not be useful. This is especially true in Canada where adding folic acid to some foods (such as flour) is required.

Scientists at Health Canada led this work. It was published in the American Journal of Clinical Nutrition (2017 May;105(5):1101-1109. doi: 10.3945/ajcn.116.137968).

Associations between various chemicals and pregnancy outcomes

Maternal exposure to perfluorinated chemicals and reduced fecundity: the MIREC study

Perfluorinated chemicals (PFCs) or perfluoroalkyl substances (PFASs) have been widely used in domestic and industrial products. This makes them resistant to:

  • stains
  • water
  • grease

These chemicals can persist in the environment. Risk management efforts have largely phased them out in the last decade due to environmental and health concerns.

Production of several PFASs has been on the decline. Still, Canadians have low levels of PFASs in their blood. This is according to recent national biomonitoring surveys in Canada.

Some PFASs are linked to adverse health effects, especially in animal models. There is conflicting evidence about the effects of PFASs on human fertility.

Some recent studies suggest that higher concentrations of PFASs may increase the time it takes to get pregnant. Other studies report no effect.

This study examined the link between PFASs and time to pregnancy. During the first study visit, women were asked how many months of unprotected sex it took them to get pregnant.

Infertility was defined as:

  • using infertility treatment for the pregnancy or
  • more than 12 months of trying to get pregnant

Maternal blood samples were assessed for 3 of the most common PFASs:

  • perfluorooctanoate (PFOA)
  • perfluorooctane sulfonate (PFOS)
  • perfluorohexane sulfonate (PFHxS)

A total of 1,743 women were included in this study. The results were adjusted for factors that could interfere with fertility, such as:

  • age
  • body mass index
  • socio-economic status

The study found that levels of PFASs were lower than levels found in previous studies. However, higher blood levels of PFOA or PFHxS were linked to an increase in the number of months to become pregnant. No significant link was observed for PFOS.

The odds of infertility increased as blood PFOA or PFHxS concentrations increased.

These results suggest that exposure to PFOA and PFHxS may affect fertility. This is true even at lower levels than those found in other studies.

This is the largest study to date on the subject. However, these results need to be read with caution.

Important factors in couple fertility were not measured. These include the health status and exposures of the male partners.

Still, these results support the measures taken to reduce the release of these pollutants into the environment.

This study involved scientists from:

  • Health Canada
  • University of Montreal
  • the Sainte-Justine University Hospital Research Centre

It was published in the journal Human Reproduction (2015 Mar 30(3):701-9).

Exposure to phthalates, bisphenol A and metals in pregnancy and the association with impaired glucose tolerance and gestational diabetes mellitus: the MIREC study

Chemicals that may disrupt the hormone system were measured to see if they increased the risk of gestational diabetes.

Levels of BPA and several phthalates were measured in women's urine. Four metals were measured in their blood:

  • lead
  • arsenic
  • cadmium
  • mercury

A glucose tolerance test was given during pregnancy. It identified women with gestational diabetes or impaired glucose tolerance.

Women were 4 times as likely to have gestational diabetes if they had high levels of arsenic in their blood. This is compared to women with low levels of arsenic in their blood.

Higher levels of the other metals showed no link to:

  • impaired glucose tolerance
  • a risk of gestational diabetes

The study's results add to the data supporting arsenic's role in increasing women's risk of gestational diabetes.

Scientists at the IWK Health Centre in Halifax led this study. This study was published in the journal Environment International (2015 Oct;83:63-71).

Associations between various chemicals and infant growth and metabolic health

A birth cohort study to investigate the association between prenatal phthalate and bisphenol A exposures and fetal markers of metabolic dysfunction

Phthalates are a group of chemicals used in many consumer products such as fragrances and plastic containers. BPA is a chemical used to make:

  • paper receipts
  • hard, clear plastic
  • a protective lining on the inside of metal-based food and drink cans

These chemicals are similar in structure to some of the hormones our bodies produce. For this reason, these chemicals may have harmful effects on the endocrine and reproductive systems.

This is of concern for pregnant women and their developing babies. This is because babies are more susceptible to possible adverse effects of environmental chemicals.

This study examined the link between:

  • metabolic function hormones and
  • pregnant women's exposure to phthalates and BPA

Comparisons were made between:

  • levels of BPA and phthalates in the women's urine and
  • the hormones, leptin and adiponectin, in umbilical cord blood

The results showed that leptin levels were higher among female infants than male infants. Adiponectin levels were about the same among males and females.

Sources of exposure to the phthalate monobenzyl may include:

  • vinyl flooring
  • food packaging

Women with higher levels of monobenzyl phthalate were slightly more likely to have higher levels of cord blood leptin. Women with high exposure to monoethyl phthalate were also slightly more likely to have higher levels of cord blood adiponectin.

This research suggests that exposures to common environmental chemicals during pregnancy may be linked to fetal metabolic function.

Recent research shows that common environmental chemicals may impact metabolism. There are possible links between environmental chemicals and the rise in:

  • rates of obesity
  • type-2 diabetes

More research is needed to assess whether:

  • the changes in hormone levels observed in this study are linked to changes in childhood growth patterns
  • these changes lead to obesity and/or type-2 diabetes

Researchers at Dalhousie University led this work, which was funded by:

  • Health Canada
  • the Canadian Diabetes Association (CDA)

This study was published in the journal Environmental Health (2014 Oct 22;13:84).

Maternal blood metal levels and fetal markers of metabolic function

This study explored the possible adverse effects of prenatal exposure to metals on hormone markers of fetal metabolism.

Past research suggests that maternal exposure to metals found in the environment may adversely affect fetal metabolism.

This study measured hormones that regulate energy intake and fat stores and examined the link between these hormones in umbilical cord blood and prenatal exposure to:

  • lead
  • arsenic
  • mercury
  • cadmium

People may be exposed to these metals through:

  • cigarette smoking
  • industrial emissions
  • pollutants in:
    • soil
    • food
    • water

The hormones measured in umbilical cord blood (leptin and adiponectin) may be able to predict childhood growth patterns.

In adults, very low levels of leptin can lead to uncontrolled feeding and weight gain. Low levels of adiponectin are linked to increased risk of diabetes and heart disease.

The study found cord blood leptin levels were higher among female infants than male infants. Cord blood adiponectin levels were about the same among males and females.

There was a greater chance of high cord blood leptin if the mother's blood had high levels of cadmium. This was compared to women with low exposure levels. The link was only found in male infants.

No significant links were found between the other metals and these hormones. The study results suggest that prenatal exposure to some metals, such as cadmium, may have an impact on fetal metabolism.

This gives reason to examine further the role of prenatal exposures to chemicals on childhood growth patterns. Further research will allow for a more complete description of their possible impact on child health and growth.

This study was done in partnership with scientists at Dalhousie University. It was published in the journal Environmental Research, (2015 Jan;136:27-34).

Maternal concentrations of perfluoroalkyl substances and fetal markers of metabolic function and birth weight

Past research suggests that higher maternal exposure to PFASs may be linked to lower infant birth weight. PFASs are persistent pollutants. They are widely used to produce common household and consumer goods, such as:

  • clothing
  • cookware
  • food packaging

The fetal period is a window of higher sensitivity to the possible adverse effects of environmental chemicals. This study examined the possible link between infant birth weight and maternal blood concentrations of 3 forms of PFASs:

  • perfluorooctanoic acid (PFOA)
  • perfluorooctanesulfonate (PFOS)
  • perfluorohexanesulfanoate (PFHxS)

The link between maternal exposure to these chemicals and umbilical cord blood levels of leptin and adiponectin was also assessed. These 2 hormones may be able to predict childhood growth patterns.

PFASs were measured in first trimester maternal blood of the MIREC women. Higher levels of PFOA in maternal blood were linked to reduced birth weight of infants. The size of this effect was small.

Maternal concentrations of PFOS were linked to a modest decrease in cord blood leptin levels.

Most North American women have detectable concentrations of these 3 types of PFASs in their blood. For this reason, it is important to continue to assess the possible health risks of these chemicals.

Tracking the MIREC children as they age will help reveal whether the observed findings can be linked to future growth and development.

Scientists from Dalhousie University led this study, with aid from Health Canada scientists. It was published in the American Journal of Epidemiology (2017 Feb 1;185(3):185-193).

Associations between various chemicals and infant immune system

Prenatal exposure to phthalates, bisphenol A and perfluoroalkyl substances and cord blood levels of IgE, TSLP and IL-33

Childhood allergies and asthma have increased in recent decades. This trend isn't fully explained by known risk factors such as family history and smoking.

The thinking has been that certain environmental chemicals may increase the risk of childhood allergic disease. These chemicals include:

  • BPA
  • PFASs
  • phthalates

Prenatal exposure to these chemicals is of great interest. This is because the fetal period is an important time for immune system development.

Disruptions to fetal immune system development may increase the risk of future childhood allergic disease. Disruptions may be marked by changes in blood levels of immune system markers, such as:

  • IgE
  • TSLP
  • IL-33

This study examined the link between umbilical cord blood levels of 3 immune system markers and prenatal exposure to:

  • BPA
  • PFASs
  • phthalates

Data from the MIREC study were used to explore this link. Of the 2,000 women studied, 1,258 met certain criteria:

  • had a term birth
  • had a single birth
  • provided a cord blood sample

There was no link between cord blood immune system markers and the 3 groups of chemicals studied. These results add to the body of knowledge that supports decisions made by Health Canada for these chemicals.

This work was led by scientists at Dalhousie University and was published in the journal Environmental Research (2015 Jul;140:360-8).

Associations between various chemicals and infant/child behaviour and neurodevelopment

Associations of prenatal urinary bisphenol A concentrations with child behaviors and cognitive abilities

Some studies have linked prenatal BPA exposure to adverse effects on children. Other studies have not found this link. Only a few prior studies of prenatal BPA exposure have assessed children's ability to learn and reason.

This study measured BPA levels in urine of pregnant women in the MIREC study.

When the children born to these women were about 3 years old, the study team measured their cognitive abilities. They did so using:

  • intelligence (IQ) tests
  • executive function tests
    • ability to plan, organize, pay attention and remember things
  • parent reports of child behaviour

BPA levels in the urine of the pregnant women were not linked to their child's IQ. However, the observed link between prenatal BPA exposure and executive function differed by child's sex.

Links were estimated for those children who had 2 times higher prenatal BPA exposure. Working memory scores were 1 point poorer in boys and 0.5 points better in girls for these children. In boys, higher maternal urine levels of BPA was also linked to some behaviours, including:

  • anxiety
  • depression
  • somatic behaviours (experiences of physical symptoms that can't be explained by underlying conditions)

Two times higher prenatal BPA was also linked to worse scores on a test that measured:

  • communication
  • interpersonal behaviours
  • repetitive or stereotypic behaviours

Prenatal BPA levels were linked to some aspects of children's behaviour and working memory. However, the researchers could not conclude that BPA caused these effects. This is because they could not adjust for parental behaviour and IQ.

BPA levels were also only measured once during the pregnancy. Still, these results add to the body of knowledge on possible neurotoxic effects linked to prenatal BPA exposure.

This work was led by scientists at Brown University and published in the journal Environmental Health Perspectives (2017 Jun 16;125(6):067008).

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