Inventory of Pregnancy and Birth Cohort Studies in Canada - December 2009

Introduction

Pregnancy and birth cohort studies are fundamental research tools to monitor children's health and development and to link prenatal and early postnatal exposures to long-term outcomes. The longitudinal perspective of these studies allows firmer causal inferences about the relationship between environmental and genetic factors to which children have been exposed and their subsequent outcomes.

New and important pregnancy/birth cohort studies have been conducted in the past years in many industrialized countries, including Canada, the United States, and several European countries. With the recent expansion of such studies in Canada, their increasingly diversified content, and the new methods of data collection they have used, many felt it was time to assess the current Canadian landscape. At a workshop organized by the Institute of Human Development, Child and Youth Health (IHDCYH) of the Canadian Institutes of Health Research and Health Canada in Ottawa last February, it was proposed to develop an inventory of pregnancy/birth cohort studies in Canada.

In discussions subsequent to the February workshop, IHDCYH partnered with the Maternal, Infant, Child and Youth Research Network (MICYRN) and the Strategic Knowledge Cluster on Early Childhood Development (SKC-ECD) to plan and develop this inventory, which built on initial efforts by MICYRN.

This document summarizes the rationale behind the inventory and its objectives, methodology, and content. Finally, it suggests a number of next steps.

Objectives

Considering the growth of pregnancy and birth cohort studies in Canada, it is important to examine the context and methods used and the kind of information available from these studies. The main objectives of this Canadian pregnancy and birth cohort inventory are to:

  • present Canadian pregnancy and birth cohort studies that are either completed or ongoing;
  • provide information on the content and design of such studies;
  • compare features of Canadian birth cohort studies, both at national and international levels;
  • identify important gaps in content that are not being addressed, or are being suboptimally addressed, by current studies;
  • provide a tool for enhanced research collaboration.

Methodology

Canadian pregnancy and birth cohort studies have been identified by reviewing PubMed and PsychInfo through a keyword search (e.g., Canada, pregnancy, birth cohort, follow-up etc). Studies have also been identified by enquiring about the research activities at research centres and institutes affiliated with Canadian universities or hospitals.

Inclusion criteria

To be included in the inventory, studies have to meet the following criteria:

  • The first wave of data collection is before conception, during pregnancy, or shortly after birth
    • Cohort studies beginning later in childhood, but with retrospective information obtained on the pregnancy or the young infant, have also been included
  • The initial sample size was at least 200 participants1
  • Retrospective and/or prospective longitudinal design, with a minimum of 2 data collection periods
  • Data are collected from mothers and/or infants living in the Canadian provinces or territories. Studies that are part of broader international initiatives are included in the inventory if this criterion is met.

Content

The content and format of this inventory was strongly influenced by previous inventories of birth cohort studies2. The data tabulated on the studies included has been gathered and entered in the inventory from a variety of available sources. For each study, the principal investigator and/or research coordinator has been asked to verify, validate, and complete the tabulated information. The initial version of this inventory is providing complete information for 46 studies. An additional 12 studies are listed at the end of the tables (in italic and bold) but only titles are provided as it was not possible to obtain, verify and validate content information for these studies.

The inventory involves both a synopsis table and a detailed table. For each table, specific data elements have been developed to describe the included studies.

For each study, the synopsis table provides:

  • Identification of the study, including:
    • Cohort name, principal investigator(s), start of enrolment, status of the study, design (i.e. whether population-based or not, coverage, initial sample size, duration of follow-up) and cohort website address
  • The period(s) when data were collected (during pregnancy; at birth; postnatal)
  • Sources of data collected, including administrative databases3, questionnaires, DNA, and other biological samples
    • Administrative data
      • Whether administrative data have been collected for the initial sample, follow-up, or entire cohort
      • Whether data have been collected on social environment measures and on birth, infant, child, and maternal outcomes
    • Questionnaire data
      • Whether questions are included on social and/or physical environmen
    • Bio-genetic samples
      • Whether DNA and other biological samples have been collected from the mother, father, and child
    • Information on whether a cohort study has used direct measures (i.e., other than by questionnaire), to assess the physical environment.and health outcomes

For each study,the detailed table provides:

  • Identifying information about the study including:
    • Cohort name, principal investigator and lead institute, status of the study, initial sample size (of mothers, fathers and children), source population (selected, hospital-based, region-based, nation-based or multi-national), inclusion and exclusion criteria, coverage, start of enrolment, gestational age at enrolment, duration of follow-up, sample size at each follow-up, and cohort website address
  • Information on the sources of data collected, including administrative data, questionnaire data, bio-genetic samples, and direct measures
    • Administrative data
        • Whether administrative data have been collected for the initial sample, follow-up, or the entire cohort
      • Questionnaire data
        • Whether questionnaires have been administered during the first, second, and third trimesters of pregnancy; at birth; and at 0-6 months, 7-18 months, 19-60 months, and 5+ years
      • Bio-genetic samples:
        • Types of biological samples collected for each of the following periods: 1st, 2nd, and 3rd trimester of pregnancy; at birth; and at 0-6 months, 7-18 months, 19-60 months, 5+ years:
          • Maternal, paternal, and offspring blood; cord blood; umbilical cord tissue; placenta; meconium; breast milk; maternal, paternal, and offspring urine; maternal, paternal, and offspring hair; maternal paternal, and offspring saliva
        • Blood sample types:
          • Serum; plasma; whole blood; red cells; white cells
        • DNA extraction
    1. Information on the physical environment measures (direct or indirect measures)4
    2. Information on whether researchers have a biobank and any possibility to share it
    3. Additional information on possibilities for research collaboration

    Both tables are provided in an Excel format. Since the detailed table contains extensive information, the Excel file provides a sheet for the entire table, as well as additional sheets with information limited to each of the following broad categories: social environment, physical environment, birth outcomes, child outcomes, maternal outcomes, and bio-genetics.

    The proposed categories for the inventory are further detailed in the following pages. Annex A presents basic descriptive categories of studies. More detailed information about the types of data collected (administrative data, questionnaires, and bio-genetic samples) can be found in Annexes B, C and D. The conceptualization of social environment and physical environment is illustrated in Annexes E and F, while birth, child and maternal outcomes are defined in Annex G. Finally, Annex H summarizes the additional information collected for each study.

    Next Steps

    Considering the enthusiastic comments received so far from many researchers contacted to complete and validate the gathered information, this inventory should be seen as a first step towards the development of a more comprehensive inventory of longitudinal studies in Canada. The inventory will be periodically updated.

    Annex A: Basic Descriptive Categories of Studies

     Identification:

    • Cohort name
    • Principal investigator(s)
    • Lead institute(s)
    • Cohort website address

    Basic description:

    • Enrolment
    • Status: in development, ongoing, completed
    • Initial sample size of mothers, fathers and children
    • Inclusion and exclusion criteria for participants
    • Gestational age at enrolment
    • Design: population-based or not
    • Source population: multi-national, nation-based, region-based, hospital-based, selected (e.g., high-risk)
    • Coverage
    • Expected duration of follow-up
    • Sample size at each follow-up
    • Information on data sources: administrative databases, questionnaires, bio-genetic samples
    • Information on exposures (genetics, social and physical environment) and outcomes (birth, infant/child, and maternal)

    Annex B: Types of Data Collected: Administrative Data

    Administrative Data:

    • Data collected for:
      • Initial sample
      • Follow-up
      • Entire cohort
    • Data collected on:
      • Social environment
      • Birth/child outcomes
      • Maternal outcomes

    Annex C: Types of Data Collected: Questionnaires

    Questionnaire Data:

    • Data collected on exposures (social and physical environment) and outcomes (birth, child, and maternal)
    • Data collected during:
      • First, second, third trimesters
      • At birth
      • At 0-6 months
      • 7-18 months
      • 19-60 months
      • 5+ years
    • Informant(s):
      • Parent(s)
      • Child
      • Professor
      • Other

    Annex D: Types of Data Collected: Bio-Genetic Samples

    Biological samples:

    • Maternal blood
    • Paternal blood
    • Offspring blood
    • Cord blood
    • Umbilical cord
    • Placenta
    • Meconium
    • Breast milk
    • Maternal urine
    • Paternal urine
    • Offspring urine
    • Maternal hair
    • Paternal hair
    • Offspring hair
    • Maternal saliva
    • Paternal saliva
    • Offspring saliva

    Samples collected at:

    • 1st trimester
    • 2nd trimester
    • 3rd trimester
    • Birth
    • 0-6 months
    • 7-18 months
    • 19-60 months
    • 5+ years

    Blood sample types:

    • Serum
    • Plasma
    • Whole blood
    • Red cells
    • White cells
    • DNA extraction

    Annex E: Exposures: Social Environment

    Social environment:

    • Demographic characteristics of parents
    • Family structure and composition
    • Social policy
    • Socio-economic status
    • Neighborhood characteristics
    • Social support
    • School environment
    • Child care
    • Parental behavior/lifestyle
    • Parenting style
    • Family climate
    • Parental health

    Annex F: Exposures: Physical Environment

    Physical environment:

    • Outdoor environment:
    • Indoor environment:
      • Indoor air pollutants
        • Asbestos, combustion by-products
      • Biological agents
        • Mold, mildew, bacteria, dust mites, pollen, pet dander, arthropods (e.g. cockroaches)
      • Pesticides
      • Chemicals contaminants in consumer products
        • Polybrominated diphenyl ethers (PBDEs)
        • Bisphenol A
        • Others
      • Food quality
        • Exposure to persistent organic pollutants (POPs)
          • PCBs, dioxins, organochlorine pesticides, mercury
        • Food packaging

      Physical environment measures:

      • Direct measures:
        • Personal monitoring
        • Biomonitoring
      • Indirect measures:
        • Data on defined areas or microenvironment

      Annex G: Birth, Child and Maternal Outcomes

      Birth Outcomes:

      • Gestational age
      • Preterm birth
      • Fetal growth (birth weight and or length for gestational age)
      • Birth defects
      • Severe neonatal morbidity
      • Mortality (miscarriage, stillbirth, infant death)

      Child Outcomes:

      • Growth (height, weight & obesity)
      • Acute and chronic illness
      • Neurocognitive development
      • Behavioral problems & mental illness
      • Language development

      Maternal Outcomes:

      • Pregnancy complications
      • Mode of delivery
      • Severe maternal morbidity
      • Maternal mental health

      Annex H: Additional Information Available

      Additional information available:

      • Whether…
        • Researchers have a biobank
        • Possibility of sharing the biobank
        • Possibility for research collection

      1. Smaller sample sizes were included for studies on special populations (such as premature babies)
      2. For the model on which this inventory has been based on, please refer to the Birthcohorts.net website.
      3. Administrative data refers also to medical records
      4. Direct measures refer to personal monitoring or biomonitoring while indirect measures refer to data available for defined areas/microenvironment or data obtained on physical environment by questionnaires