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6B Preterm Birth Rate

Description | Specific Indicators | Ontario Public Health Standards | Corresponding Health Indicator(s) from Statistics Canada and CIHI | Corresponding Indicator(s) from Other Sources | Data Sources |  Alternative Data Sources |  Analysis Check List | Method of Calculation |  Basic Categories | Indicator Comments | Definitions | Cross-References to Other Indicators | Cited References  | Other References | Changes Made | Acknowledgements

  • The ratio of live births with a gestational age at birth of less than 37 completed weeks, per total live births.
Specific Indicators
  • Preterm birth rate
Ontario Public Health Standards (OPHS)
The Ontario Public Health Standards (OPHS) establish requirements for the fundamental public health programs and services carried out by boards of health, which include assessment and surveillance, health promotion and policy development, disease and injury prevention, and health protection. The OPHS consist of one Foundational Standard and 13 Program Standards that articulate broad societal goals that result from the activities undertaken by boards of health and many others, including community partners, non-governmental organizations, and governmental bodies. These results have been expressed in terms of two levels of outcomes: societal outcomes and board of health outcomes. Societal outcomes entail changes in health status, organizations, systems, norms, policies, environments, and practices and result from the work of many sectors of society, including boards of health, for the improvement of the overall health of the population. Board of health outcomes are the results of endeavours by boards of health and often focus on changes in awareness, knowledge, attitudes, skills, practices, environments, and policies. Boards of health are accountable for these outcomes. The standards also outline the requirements that boards of health must implement to achieve the stated results. 

Outcomes Related to this Indicator 
  • Board of Health Outcome (Reproductive Health): The board of health is aware of and uses epidemiology to influence the development of healthy public policy and its programs and services for the promotion of reproductive health.
  • Board of Health Outcome (Foundational Standard): The public, community partners, and health care providers are aware of relevant and current population health information, assessment and/or surveillance requirements related to this indicator.
Assessment and Surveillance Requirements Related to this Indicator (Reproductive Health) 
  • The board of health shall conduct epidemiological analysis of surveillance the area of reproductive health outcomes. 


Corresponding Indicator(s) from Statistics Canada and CIHI 
  • Pre-term births -live births with a gestational age less than 37 weeks, expressed as a percentage of all live births (gestational age known).

In: Health Indicators:
Click on "view" beside "Free", "Latest issue".
Click on "Data tables, maps and fact sheets" on the left side menu.
Click on "Birth-related indicators" ""under Health Status, Health Conditions.


Corresponding Indicator(s) from Other Sources  
  • Canadian Perinatal Surveillance System: Rate of preterm births among single and multiple live births.


Data Sources (see Resources: Data Sources) 
Note that 3 data sources are listed for use: 1) Vital Statistics, 2) Hospitalization, 3) BORN. The choice of data source will depend upon data quality within a health unit as well as data access and the specific analysis questions. For information related to the data sources, refer to the Data Source resources and the Reproductive Health Core Indicators Documentation Report

Alternative 1
Numerator & Denominator: Vital Statistics Live Birth Data
Original source: Vital Statistics, Office of Registrar General (ORG), ServiceOntario
Distributed by: Ontario Ministry of Health and Long-Term Care (MOHLTC): IntelliHEALTH ONTARIO (IntelliHEALTH)
Suggested citation (see Data Citation Notes): Ontario Vital Statistics Live Birth Data [years], Ontario Ministry of Health and Long-Term Care, IntelliHEALTH ONTARIO, Date Extracted: [date].

Alternative 2

Numerator & Denominator: Hospitalization Data
Original source: Discharge Abstract Database (DAD), Canadian Institute for Health Information (CIHI)
Distributed by: Ontario Ministry of Health and Long-Term Care (MOHLTC): IntelliHEALTH ONTARIO (IntelliHEALTH)
Suggested citation (see Data Citation Notes): Inpatient Discharges [years], Ontario Ministry of Health and Long-Term Care, IntelliHEALTH ONTARIO, Date Extracted: [date].

Alternative 3
Numerator & Denominator: BORN Information System
Original source: Better Outcomes Registry Network (BORN) Ontario
Distributed by: Better Outcomes Registry Network (BORN) Ontario
Suggested citation (see Data Citation Notes):  BORN Information System [years], Date Extracted: [date].

Alternative Data Sources 
  • Integrated Services for Children Information System (ISCIS) – Note: determine the level of completion in your health unit
Analysis Check List  
  • Exclude stillbirths
  • The IntelliHEALTH licensing agreement does not require suppression of small cells, but caution should be used when reporting at a level that could identify individuals, (e.g. reporting at the postal code level by age and sex). Please note that privacy policies may vary by organization. Prior to releasing data, ensure adherence to the privacy policy of your organization.
  • Aggregation (e.g. combining years, age groups, categories) should also be considered when small numbers result in unstable rates.
  • Exclude births to mothers that reside out-of-province. Births to Ontario mothers that occur out-of-province are not included in the data.
  • Include all births, not just those for mothers aged 15-49 years.
  • Include live births with birth weights <500g. For more information, refer to the Reproductive Health Core Indicators Documentation Report.
  • HELPS Data: Historically, PHUs obtained data for live births, stillbirths, therapeutic abortions, congenital anomalies, and deaths from the Ministry of Health through HELPS (the HEalthPlanning System). Although these data are no longer commonly used, some PHUs may still be accessing these data files. Information about the data can be found in the HELPS Data Source resource.
Vital Statistics 
  • In IntelliHEALTH under Standard Reports, folder "01 Vital Stats", open "Birth Summary V2". This report summarizes information on births by age group and mother's residence (Ontario, PHU and LHIN). IntelliHEALTH also provides population data (total population, female population aged 15-49 years) for the calculation of rates. Refer to the Notes tab for information. Open "1.2 Births x PHU x Type x Age" to obtain public health unit data and "1.1 ON Births x Type x Age" to obtain Ontario data. This standard report does not include gestational age. To add this variable, Edit the report > Data > Select Data and choose "Pregnancy Duration" under Birth Information. The report can be modified, renamed and saved under your own folder or can be exported into Excel. Alternatively a new report can be created with the required variables.
  • The predefined report provides birth and population data for the calendar years from 1986 to the most recent available. Table options can be edited to change the number of years of data presented. For years that are not displayed modify the calendar year filter to include the required years.
  • Type of birth includes the categories single birth, twins, triplets, quadruplets, quintuplets with each broken down by live births and stillbirths, and summed for total births.
  • The data contained in the Birth Summary v2 report includes births to Ontario mothers in Ontario only.
  • The notes section of the report provides important data caveats and information and should be consulted. Refer to the Vital Statistics Live Birth Data Source and Vital Statistics Stillbirth Data Source for more information about the data. 
  • Under the Inpatient Discharge Main Table data source from the ‘05 Inpatient Discharges' folder, use the "Hospital births x births, delivery type" predefined report. This report can be modified, renamed and saved under your own folder.
  • The report provides hospital birth counts (Admit Entry Type = N for Newborn or S for Stillbirth) for Ontario and by PHU, including only Ontario residents (Patient Province equal to ON).
  • The calendar year for date of admission is used (Admit CYear) rather than date of discharge since the date of admission will be the same as the birthdate for newborns.
  • Even though counts are grouped by calendar year of admission, it is the actual number of discharges that are counted.
  • Edit the report to add field "Gestation Age" from Patient Information.
  • Gestation Age is available for CY2006 onwards.
BORN Information System 
  • Public Health Units access BORN data through public health reports and data cubes. 
  • Refer to the BORN Information System resource for more information about the data.
Method of Calculation

Rate of Preterm Births:

total number of live births delivered <37 weeks completed gestation 

x 100

total number of live births


Basic Categories  
  • Type of birth (single, multiple)
  • Length of gestation: <32 completed weeks (very preterm), 32 to less than 37 completed weeks (moderate/late preterm), 37 to less than 42 completed weeks (term), ≥42 completed weeks (postterm)
  • Geographic areas of patient residence:
    • Vital Statistics, Hospitalization data: Ontario, public health unit, municipality, and smaller areas of geography based on aggregated postal code.
    • BORN data: Ontario, public health unit
Indicator Comments
  • Preterm (or premature) birth is the leading cause of neonatal and infant mortality in Canada and industrialized countries (1,2).
  • After adjusting for other factors, preterm birth is most strongly associated with multiple birth status, the maternal conditions of diabetes and hypertension, and previous preterm deliveries. (3)
  • Other risk factors for preterm birth include mother's age (<20 or >35 years), primiparous (first delivery), single marital status, smoking, high perceived stress, illicit drug use, low pre-pregnancy weight, low or high weight gain, and race/ethnicity (2, 3).
  • Fertility treatments may affect the multiple birth rate and thus the preterm birth rate.
  • The preterm birth rate has been steadily increasing in Canada and many industrialized countries. The increased rate has been primarily due to an increase in moderate and late preterm births (3, 4). The increased incidence of near-term infants has large health care resource consequences (5).
  • The very preterm category (<32 completed weeks gestation) could be further divided into the <28 completed weeks (extremely preterm) and 28 to <32 completed weeks because of the much higher morbidity and mortality that occurs among those infants born before 28 weeks (3). However, since the number of infants born at this gestation is small, particularly at the health unit level, it is more practical to report rates for very preterm infants or total preterm infants.
  • The postterm birth rate is defined as the proportion of live births that occur at a gestational age of 42 or more completed weeks of pregnancy. Postterm births are associated with increased maternal complications and perinatal morbidity and mortality compared to term pregnancies (2). Postterm birth can be prevented through clinical management, e.g. inducing labour, caesarian delivery, and is less of a public health issue than preterm birth. Generally, less than 1% of births are postterm; rates are decreasing (2).
  • Gestational age data can be affected by recall errors, post-conception bleeding, irregular or long/short menstrual cycles, delayed ovulation, pregnant women or partner's desires to indicate a later conception, and unrecognized fetal loss. These types of errors with gestational age data have become less of an issue in the last decade with the increasing use in Ontario of early ultrasound technology to estimate length of gestation (6).
  • Gestational age has been described as being more accurate with ultrasound technology (especially for under 12 weeks of fetal age) but ultrasound may not be used in all regions, also, the method used to determine GA is not well-recorded in databases (7,8).
  • If using Vital Statistics data, inconsistencies in the source for gestation information overestimated preterm births from 1990 to 1998. Refer to Vital Statistics Live Birth Data Source for more information.
  • Gestational age - calculated as the interval between the date of delivery of the fetus or newborn and the first day of the mother's last normal menstrual period. Full-term pregnancies average about 40 weeks (37 completed weeks to 42 completed weeks).
  • Live birth - the complete expulsion or extraction from its mother of a product of conception, irrespective of the duration of the pregnancy, which, after such separation, breathes or shows any other evidence of life such as heartbeat, umbilical cord pulsation, or definite movement of voluntary muscles, whether the umbilical cord has been cut or the placenta is attached. A live birth is not necessarily a viable birth.
  • Multiple birth - occurs when a pregnancy results in the development of two or more fetuses.
  • Pregnancy - the gestation process, from conception through to the expulsion of the product of conception from the body whether through miscarriage, therapeutic abortion, caesarean section, or vaginal delivery.
  • Preterm birth - a live birth that occurs at less than 37 completed weeks (i.e., <259 days) of gestation (2).
  • Postterm birth - a live birth that occurs at 42 or more completed weeks (i.e., ≥294 days) of gestation (2).
  • Very preterm birth - a live birth that occurs before the end of the 32 completed weeks (i.e., <224 days) of gestation (1).
  • Moderate/late preterm birth - a live birth that occurs between 32 completed weeks (i.e., ≥224 days) and 37 completed weeks (i.e., <259 days) of gestation (1).
Cross-References to Other Indicators
Cited References
  1. Kramer MS, Demissie K, Hong Y, Platt RW, Sauve R, Liston R. The contribution of mild and moderate preterm birth to infant mortality. JAMA. 2000;284(7):843-9. Available from: Accessed on March 23, 2012.
  2. Public Health Agency of Canada. An Overview of Perinatal Health in Canada in Canadian Perinatal Health Report, 2008 Edition. Ottawa, 2008. Available from: Accessed on March 23, 2012.
  3. Canadian Institute for Health Information. Too Early, Too Small: A Profile of Small Babies Across Canada. 2009. Ottawa, ON, Canadian Institute for Health Information. Available at: Accessed on March 23, 2012.
  4. BORN Ontario. Perinatal Health Report 2008 - Public Health Reports. May 2010. Available from: Accessed on March 23, 2012.
  5. Wang ML, Dorer DJ, Fleming MP, Catlin EA. Clinical outcomes of near-term infants. Pediatrics. 2004;114(2):372-376. Available from: Accessed on November 2, 2012.
  6. You JJ, Alter DA, Stukel TA, McDonald SD, Laupacis A, Liu Y, Ray JG. Proliferation of prenatal ultrasonography. CMAJ. 2010 Feb 9;182(2):143-51.
  7. Callaghan WM, Dietz PM. Differences in birth weight for gestational age distributions according to the measures used to assign gestational age. Am J Epidemiol. 2010; 171 (7):826-36.
  8. Shore R. KIDS COUNT Indicator Brief: Preventing Low Birth Weight. Baltimore: Annie E. Casey Foundation; 2009. Available from:
Other References
  • Health Canada. Perinatal Health Indicators for Canada: A Resource Manual. Ottawa: Minister of Public Works and Government Services Canada, 2000. Available from: Accessed on September 14, 2012.
  • Durham Region Health Department. Focused Report on Preterm Births in Durham Region. September 2009. Available from: Accessed on March 23, 2012.
Changes Made
DateType of Review - Formal or Ad HocChanges Made ByChanges Made
March 2010FormalReproductive Health Sub-GroupReplaced Mandatory Health Programs section with updated Ontario Public Health Standards outcomes.
March 30, 2012 - January 16, 2013FormalReproductive Health Sub-Group

·      Three data sources cited with analysis check-list for each.
·      All births included - no longer exclude births with birth weight less than 500g.
·      Post-term birth rate was removed as a specific indicator and was incorporated as a category within gestation.



Lead Authors

  • Jessica Deming, Region of Waterloo Public Health
  • Mary-Anne Pietrusiak, Durham Region Health Department

Contributing Authors

  • Reproductive Health Sub-Group


  • Sherri Deamond, Durham Region Health Department (Core Indicators Work Group member)
  • Suzanne Fegan, Kingston Frontenac Lennox and Addington Public Health, (Core Indicators Work Group member)
  • Virginia McFarland, Grey Bruce Health Unit
  • Paula Stewart, Leeds Grenville and Lanark District Health Unit
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