To advance and promote the discipline and professional practice
of public health epidemiology in Ontario

Birth Weights Core Indicator

  • The rate of live births in a specified weight range at the time of delivery per total live births.
  • Weight in relation to gestational age, reported using a reference population and specific percentile cut-offs.
Report an IssueAppendices

Related OPHS Topics

Reproductive Outcomes
 

Method of Calculation

Low Birth Weight Rate for Live Births
total number of live births weighing < 2,500 grams
100
total number of live births
100
 
Low Birth Weight Rate for Singleton Full-term Live Births
total number of singleton live births, 37+ weeks gestation, weighing < 2,500 grams
100
total number of singleton live births, 37+ weeks gestation
100
Very Low Birth Weight Rate for Live Births
total number of live births weighing < 1,500 grams
100
total number of live births
100
 
Extremely Low Birth Weight Rate for Live Births
total number of live births weighing < 1,000 grams
100
total number of live births
100
 
Small for Gestational Age
total number of singleton live births with weights below the 10th percentile of birth weights for their gestational age and sex*
100
total number of singleton live births
*Gestational age calculations are sex-specific, see Analysis Checklist for full details.
100
 
Large for Gestational Age
total number of singleton live births with weights above the 90th percentile of birth weights for their gestational age and sex*
100
total number of singleton live births
*Gestational age calculations are sex-specific, see Analysis Checklist for full details.
100

Recommended Subset Analyses

Birth Weight
  • low
  • very low
  • extremely low
Weight in relation to gestational age (i.e., SGA, LGA)
  • relevant only to singletons with gestational ages 22-43 completed weeks.
Type of birth
  • single
  • multiple
Geographic areas of patient residence
  • Ontario , public health unit, municipality, and smaller areas of geography based on aggregated postal code.
  • TA data does not contain postal code.
  • BORN data: Ontario, public health unit

Data Sources

Numerator & Denominator: Option 1
Numerator & Denominator: Option 2 
 Numerator & Denominator: Option 3
Vital Statistics Live Birth Data

Original Source:

Vital Statistics, Office of Registrar General (ORG), Service Ontario

Distributed by:

Ontario Ministry of Health and Long-Term Care (MOHLTC): IntelliHEALTH Ontario (IntelliHEALTH)

Suggested Citation:

Ontario Vital Statistics Live Birth Data [years], Ontario Ministry of Health and Long-Term Care, IntelliHEALTH ONTARIO, Date Extracted: [date].
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:

Inpatient Discharges [years], Ontario Ministry of Health and Long-Term Care, IntelliHEALTH ONTARIO, Date Extracted: [date].
BORN Information System

Original Source:

Better Outcomes Registry Network (BORN) Ontario

Distributed by:

Better Outcomes Registry Network (BORN) Ontario

Suggested Citation:

BORN Information System [years], Date Extracted: [date].


Analysis Checklist  

General Checklist
  • 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 weight <500 g. For more information, refer to the Reproductive Health Core Indicators Documentation Report.
  • Births with unknown or missing birth weight should be excluded from analysis. 
  • 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.
Calculating Weight in Relation to Gestational Age
  • SGA and LGA calculations apply to singletons of 22-43 weeks gestation (see Indicator Comments).
  • Births with unknown or missing gestational age should be excluded from SGA/LGA analysis (2).
  • The cut-offs used in the weight for gestational age calculations must be sex-specific. The number of females outside the female range must be calculated separately and added to the corresponding number for males in order to get the total.
  • It is also important to note that the cut offs and calculated rates will vary depending on the reference table that is used to obtain the values for the percentiles. The current Canadian reference percentile tables can be found at http://www.phac-aspc.gc.ca/rhs-ssg/bwga-pnag/pdf/bwga-pnag_e.pdf.
  • The convention is to use the 10th percentile for "Small for Gestational Age" and the 90th percentile for "Large for Gestational Age". However, 5th and 95th as well as the 3rd and 97th percentiles have also been used depending on the specificity and sensitivity needed for the calculation. Note that the 5th and 95th and the 3rd and 97th percentile cut-offs for SGA and LGA identify increasingly high-risk babies, as compared to the 10th and 90th percentile cut-offs.

Vital Statistics
  • A predefined report has been created in IntelliHEALTH under Standard Reports, folder "50 APHEO Public Health Indicators". Open "Vital Stats Live Births - data for SGA, LGA calculations". This report will download data required for calculating singleton, live births that are SGA or LGA. Refer to the Notes tab for information, including extraction criteria. The report can be modified, renamed and saved under your own folder or can be exported into Excel, and then imported into a statistical package such as STATA, SPSS or SAS. Syntax files are then required to calculate SGA and LGA variables. 
  • The predefined report provides live birth data for the calendar years 1986 to the most recent available. You will be prompted to provide the year(s) and PHU(s).
  • The data contained in the predefined report includes births to Ontario mothers in Ontario only.
  • The notes section of the report provides important data caveats and background information on data sources and should be consulted.
  • Ontario birth data information suffered data quality issues in the 1990s and many of these have been addressed. Refer to the Vital Statistics Live Births  and Vital Statistics Stillbirth Data Sources for more information about the data.

Hospitalization
  • Predefined reports have been created in IntelliHEALTH under Standard Reports, folder "50 APHEO Public Health Indicators'. There is the static report "Births – small-, large-for-gestational age - PHU 2006-[most recent year]" and the predefined report "Hospital Births – data for SGA, LGA Calculations.
  • Alternatively, under the Inpatient Discharge Main Table data source from the ‘05 Inpatient Discharges' folder, use the "Hospital Births" 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.
  • Select the appropriate calendar years, PHU, and "Newborn - Born Alive in Reporting Institution" (exclude stillborn infants) as prompted from the pre-defined filters.
  • The first tab provides the number of births by infant weight group. If choosing to examine birth weights less than 500 g separately, edit table to exclude live births with birth weight less than 500g by choosing Infant Weight Group not equal to 1.
  • Even though counts are grouped by calendar year of admission, it is the actual number of discharges that are counted. 
  • When analyzing birth weight information, gestational age and multiple birth status are also important. Refer to the Preterm births indicator and Multiple births indicator.
  • An SPSS syntax file is available for calculating SGA and LGA. See SGA-LGAsyntax.sps.
  • Note that hospitalization data do not include home births and other non-hospital births, which together may account for approximately 2% of total births (4).

BORN
  • Public Health Units access the BORN data through public health reports or data cubes.
  • Refer to the BORN Information System resource for more information about the data.

Indicator Comments

General Comments
  • While low birth weight is still an important birth outcome measure, birth weight is best considered within the context of gestational age (GA) despite potential challenges with establishing gestational age; that is, constitutionally small babies are not all undersized when important associations are taken into account (5-7).
  • 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 (8).
  • 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 (5,9).
  • Implausible birth weight for gestational age combinations can be cleaned using biostatistical methods to create reports and standardized tables (10-12).
  • Low birth weight may be associated with premature birth or slow growth of the fetus or both, but each issue has different public health implications. Low birth weight was a common proxy measure of infant morbidity and mortality, and is still used for cross-country comparisons (13). 
  • Low birth weight is often used as a proxy indicator to quantify the magnitude of fetal growth issues in developing countries because valid assessment of gestational age is generally not available (14).
  • Analyzing birth outcome trends in relation to maternal age provides valuable data relevant to population health. 
  • If choosing to calculate appropriate weight for gestational age (AGA), note that the method of calculation may vary depending on the percentile reference population that was used. It may also vary depending on which percentile cut offs were used to define AGA (some use 10th - 90th, others use 5th - 95th or 3rd - 97th depending on the sensitivity and specificity required) (15).
  • Prematurity is the leading cause of death among newborn babies (13).
  • The effects of premature birth and multiple gestation (e.g. twins) on birth weight distributions can be eliminated by using only full term singleton live births. Stratify by singleton and higher order births in the analysis (16).
  • Birth weight is affected by many factors such as mother's age, birth intervals, type of birth (i.e. multiple), gestational age, parity, lifestyle factors (e.g. smoking), weight gain during pregnancy, physical and social environment,  intrauterine infection, diabetes mellitus, low SES, genetic factors and more (17).
  • Mother's age is recorded at time of delivery.
  • Large for gestational age predicts those who are at increased risk of insulin resistance and metabolic syndrome associated with health problems such as obesity later in life (18).
  • Canadian reference birth weight for gestational age percentile cut-offs from Kramer et al (1) may misclassify healthy infants of certain ethnicities as SGA. Newborns of parents originating from non-European/Western nations tend to be smaller at birth (10). However, ethnic-specific birth weight for gestational age cut-offs are currently not available for Ontario in a format that can be used for population health. As a result, public health units with large immigrant populations may observe higher small for gestational age rates and lower large for gestational age rates in comparison to other public health units. For more information on how this may affect SGA and LGA rates within a specific PHU population, refer to articles by Ray et al (10) and Urquia (12).
  • Birth weight for gestational age reference percentile cut-offs reflect what is small, large or appropriate based on the data used to create the reference. SGA rates below 10% and/or LGA rates above 10% indicate that the population being analysed has infants with larger birth weights for gestational age than that of the reference population. SGA rates above 10% and/or LGA rates below 10% indicate the population being analysed has infants with smaller birth weights for gestational age than the reference population.
  • Birth weight for gestational age has been increasing in Canada. SGA rates have on a decreasing trend between 1995 to 2004, while LGA rates increased over the same time period (2).


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References

Definitions

Birth weight - the weight of a fetus or infant at the time of delivery. For live births, birth weight should be measured within the first hour of life, however measures in the first 24 hours are acceptable (19). 

Extremely low birth weight - less than 1,000 grams. Contrast with small for gestational age (19).  

Gestation - begins from conception through to the expulsion of the product of conception from the body whether through miscarriage, therapeutic abortion, caesarean section, or vaginal delivery.

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).

Large for gestational age (LGA) - the birth weight of an infant that falls above the 90th percentile of appropriate for gestational age infants, specific to the length of gestation (1). Also called large for dates (20). Kramer et al. propose sex-specific weights based on gestational age, with large for gestational age being those infants born at the 90th percentile or above (1, 21). For example, 40 week infants weighing more than 4,200 g (males) and 4,034 (female) would be LGA (1).

Low birth weight - less than 2,500 grams or 5 pounds 8 ounces. Contrast with small for gestational age.

Pregnancy - the gestation process, from conception through to the expulsion of the product of conception from the body whether through miscarriage, therapeutic abortion, cesarean section, or vaginal delivery.

Preterm birth - a live birth that occurs at less than 37 completed weeks (i.e., <259 days) of gestation. 

Small for gestational age (SGA) - the birth weight of an infant that falls below the tenth percentile of appropriate for gestational age infants, specific to the length of gestation. Also called small for dates (20). Kramer et al. propose sex-specific weights, based on gestational age (1, 21). For instance, 40 week old infants weighing less than 3,079 g (males) or 2,955 g (females) would be SGA (1). Contrast with low birth weight. 

Appropriate weight for gestational age (AGA) -  a fetus or newborn infant whose size is within the normal range his or her gestational age.  This would include infants with birth weights for gestational age that are greater than the 10th percentile cut off but less than the 90th percentile cut off (22).

Very low birth weight - less than 1,500 grams or 3 pounds 5.5 ounces (19).

Cited References
  1. Kramer MS, Platt RW, Wen SW, Joseph KS, Allen A, Abrahamowicz M, et al. A new and improved population-based Canadian reference for birth weight for gestational age. Pediatrics. 2001; 108(2).
  2. Public Health Agency of Canada. Canadian Perinatal Health Report, 2008 Edition. Ottawa, 2008. Available from: http://www.phac-aspc.gc.ca/publicat/2008/cphr-rspc/pdf/cphr-rspc08-eng.pdf
  3. Health Canada. Perinatal Health Indicators for Canada: A Resource Manual. Ottawa, Minister of Public Works and Government Services Canada, 2000. Available from: http://publications.gc.ca/collections/Collection/H49-135-2000E.pdf.
  4. Statistics Canada. Births 2006. Statistics Canada Catalogue no. 84F0210X. 2008. Ottawa, ON.  Available from: http://www.statcan.gc.ca/pub/84f0210x/84f0210x2008000-eng.pdf
  5. 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.
  6. Canadian Institute for Health Information. Too early too small. Ottawa: CIHI, 2009. Available from: https://secure.cihi.ca/free_products/too_early_too_small_en.pdf. Accessed Jan 4, 2010.
  7. Parker J, Klebenoff, M. Invited commentary: crossing curves - it's time to focus on gestational age-specific morbidity. Am J Epidemiol. 2009; 169 (7):798-801.
  8. 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.
  9. Shore R. KIDS COUNT Indicator Brief: Preventing Low Birth Weight. Baltimore: Annie E. Casey Foundation; 2009. Available from: http://www.aecf.org/KnowledgeCenter/Publications.aspx?pubguid=%7B950E85EE-C2B4-466E-AA20-AE2010384A17%7D
  10. Ray JG, Sgro M, Mamdani MM, Glazier RH, Bocking A, Hilliard R, Urquia ML. Birth weight curves tailored to maternal world region. J Obstet Gynaecol Can. 2012; 34(2): 159-171.Available from: http://www.jogc.com/abstracts/201202_Obstetrics_5.pdf
  11. Platt R. The effect of gestational age errors and their correction in interpreting population trends in fetal growth and gestational age-specific mortality. Semin Perinatol. 2002; 26 (4): 306-311.
  12. Urquia ML, Ray JG. Seven caveats on the use of low birthweight and related indicators in health research. J Epidemiol Comm Hlth. July 2012.
  13. Centers for Disease Control and Prevention (CDC). Reproductive and birth outcomes and the environment. Available from: http://ephtracking.cdc.gov/showRbBirthOutcomeEnv.action. Retrieved July 3 2011.
  14. US Agency for International Development (USAID). Percent of low birth-weight singleton live births, by parity. Available from: http://www.cpc.unc.edu/measure/prh/rh_indicators/specific/nb/percent-of-low-birth-weight-singleton-live-births. Accessed July 3 2011.
  15. Xu H, Simonet F, Luo ZC. Optimal birth weight percentile cut-offs in defining small- or large-for-gestational-age. Acta Paediatr. 2010; 99 (4):550-5.
  16. Joseph KS, Fahey J, Platt RW, Liston RM, Lee SK, Sauve R, et al. An outcome-based approach for the creation of fetal growth standards: do singletons and twins need separate standards? Am J Epidemiol. 2009; 169 (5):616-24.
  17. Shah P, Ohlsson A. Literature review of low birth weight, including small for gestational age and preterm birth. Evidence Based Neonatal Care and Outcomes Research, Dept. of Pediatrics, Mount Sinai Hospital. Toronto Public Health: Toronto, 2002.
  18. Boney C, Verma A, Tucker R, Vohr B. Metabolic syndrome in childhood: association with birth weight, maternal obesity and gestational diabetes. Pediatrics. 2005;115 (3):e290-6. Available from: www.pediatrics.org/cgi/content/full/115/3/e290
  19. WHO Statistical information System, 2008. Available from: http://www.who.int/whosis/indicatordefinitions/en/
  20. Ounsted M, Moar VA, Scott, A. Risk factors associated with small-for-dates and large-for-dates infants. BJOG: An International Journal of Obstetrics & Gynaecology. 1985; 92: 226-232. doi: 10.1111/j.1471-0528.1985.tb01087.x
  21. Statistics Canada. Health Status. Health Indicators. 2010. Available from: http://www.statcan.gc.ca/pub/82-221-x/2011002/def/def1-eng.htm#hc1sfg.
  22. National Institutes of Health, US National Library of Medicine. Appropriate for Gestational Age: Medline Plus Medical Encyclopedia. Medline Plus. October 23, 2012.  Accessed October 27, 2012. Available from: http://www.nlm.nih.gov/medlineplus/ency/article/002225.htm.

Other References
  • Arbuckle TE, Wilkins R, Sherman GJ. Birth weight percentiles by gestational age in Canada. Obstetrics & Gynecology. 1993; 81(1): 39-48.
  • Bienefeld M, Woodward GL, Ardal S. Underreporting of live births in Ontario: 1991- 1997. Central East Health Information Partnership, February 2001. Available from: resources/indicators/UnderreportingOfLiveBirths.PDF.
  • Joseph KS, Kramer MS. Recent trends in Canadian infant mortality rates: the effect of changes in registration of live newborns weighing less than 500g. CMAJ. 1996; 155:1047-52.
  • Kohn MA, Vosti CL, Lezotte D, Jones RH. Optimal gestational age and birth-weight cutoffs to predict neonatal morbidity. Med Decis Making. 2000; 20(4):369-76.
  • Lubchenco LO, Hansman C, Dressler M, Boyd E. Intrauterine growth as estimated from liveborn birth-weight data at 24 to 42 weeks of gestation. Pediatrics. 1963;32:793-800.
  • Public Health Agency of Canada. Canadian Perinatal Health Report 2008 Edition. Available from: http://www.phac-aspc.gc.ca/publicat/2008/cphr-rspc/pdf/cphr-rspc08-eng.pdf

Acknowledgements

Lead Authors

Amira Ali, Ottawa Public Health

Hilary Cardarelli, University of Waterloo

Nicole Findlay, University of Toronto, former PHO practicum student

Lorraine Telford, formerly with PHO

Reviewers

Deborah Carr, Oxford County Health Unit

Sherri Deamond, Durham Region Health Department (Core Indicators Work Group Member)

Joel Ray, St. Michael's Hospital

Marcelo Urquia, St. Michael's Hospital

Carmen Yue, Toronto Public Health

Contributing Authors

Reproductive Health Sub-group

 

Revision History

 This Core Indicator Product webpage is maintained by the Reproductive Health Subgroup.  
Date Review Type Author Changes PDF
March 2010 Formal Review Reproductive Health Sub-Group
  • Replaced Mandatory Health Programs section with updated Ontario Public Health Standards outcomes.
March 1, 2012 - January 16, 2013 Formal Review Reproductive 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
  
January 14, 2014 Ad hoc Mary-Anne Pietrusiak
  • Added information about IntelliHEALTH predefined report for Vital Statistics live births data to create a dataset that can be used to calculate SGA and LGA.
  
 January 16, 2014  Ad hoc  Mary-Anne Pietrusiak
  • Updated the SPSS syntax file (SGA-LGAsyntax.sps) as modified by Amira Ali. This file has variable names that are consistent with the newest predefined report on IntelliHEALTH that downloads the data for the SGA and LGA calculations.
September 8, 2019 
Website Update:
No Content Review  
Caitlyn Paget, 
on behalf of the CIWG 
    No changes made to indicator definitions.
    Migrated to new website structure and format, including:
  • Reorganized content to provide high-level information at a glance, and move in-depth analytic information into dedicated sections for users to access when needed.
  • Renamed "Basic Categories" section to "Recommended Subset Analysis Categories"; "Definitions" renamed to "Glossary".
  • Replaced both "Cross-References to Other Indicators" and "OPHS" sections with "Related OPHS Topics" to crosslink with relevant Core Indicators webpages including OPHS program standard(s) and associated indicator(s).
  • Added descriptive sub-headings to the Analysis Checklist and Indicator Comments sections.
  • Removed "Corresponding Health Indicator(s) from Statistics Canada and CIHI" and "from Other Sources" sections.
  • Updated Revision History table, and added PDF copy of previous version for reference.
  

 



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