Methodological Notes – Reproductive Outcomes Module

Updated: April 2012

Concepts and Definitions

An important measure of reproductive outcome, the survival of the fetus while still in utero and also shortly after birth, is reflected in the number and rates of perinatal deaths. The definition of the perinatal period and perinatal death has been plagued by highly variable definitions across national jurisdictions.

WHO defines the perinatal period as commencing at 22 completed weeks (154 days) of gestation, and ends at 7 completed days after birth. This definition dates from ICD-10 and is recommended in its guidelines for reproductive health indicators.

Perinatal death is thus a death (of a fetus or a neonate) within this perinatal period. WHO also specifies that the fetus should weigh at least 500 grams or has a crown-heel length of 25 cm or more.

A neonate who dies between birth and 7 completed days clearly had to be born alive first, and counted originally as a livebirth. The WHO definition of a fetal death:

Death prior to the complete expulsion or extraction from its mother of a product of conception, irrespective of the duration of pregnancy; the death is indicated by the fact that after such separation the fetus does not breathe or show any other evidence of life, such as beating of the heart, pulsation of the umbilical cord, or definite movement of voluntary muscles (WHO Reproductive Health Indicators, 2006:32).

Fetal death is the preferred term, and should replace others such as “stillbirth”, “miscarriage” or “spontaneous abortion”. Fetal deaths do not include induced terminations of pregnancy (induced abortions).

WHO’s “22 weeks” definition is adhered to by Denmark, Finland, and Iceland; Norway starts registering fetal deaths at 12 weeks, most but not all Canadian provinces/territories and American states at 20 weeks, and Sweden at 28 weeks (until 2008, when it too adopted the 22 weeks definition). Such inconsistency has led to the recommendation to report late fetal deaths (gestation of 28+ weeks and/or birthweight of 1, 000+ grams) in international comparisons. Most national statistical agencies do report different sets of perinatal mortality data corresponding to definitions of 28+ weeks, 20+ weeks, or some other gestational age.

In CircHOB:

Late fetal deaths (LaFe) = fetal deaths of 28 weeks or more gestation

Early neonatal deaths (EaNe) = deaths during day 0 to day 6

Perinatal deaths = LaFe + EaNe

Late fetal death rate = (number of late fetal deaths in year X) / (sum of livebirths and late fetal deaths in year X)

Perinatal mortality rate = (sum of late fetal deaths and early neonatal deaths in year X) / (sum of livebirths and late fetal deaths in year X)

Both rates are expressed as per 1, 000 total births. Rates for 2000-04 and 2005-09 are calculated by dividing the sum of deaths during the 5-year period by the sum of livebirths and late fetal deaths in the same 5-year period.

The birthweight of an infant provides a gross, but easily obtainable, summary measure of the state of health and nutrition of the fetus while in utero. The distribution of livebirths by birthweight gives rise to estimates of the prevalence of low birthweight and high birthweight births. Increasingly, birthweight is recognized as a strong predictor of the development of adult chronic diseases such as heart disease and diabetes.

There is general agreement on the various low birthweight categories among international (eg. WHO Statistical Information System) and national agencies (eg. the CDC Pregnancy Nutrition Surveillance System). High birthweight has not been a concern of WHO, but among the developed countries, it is also a target of monitoring because of its association with childhood obesity.

Low birthweight (LBW): <2, 500 grams Very low birthweight (VLBW): <1, 500 grams Extremely low birthweight: <1, 000 grams High birthweight (HBW): >4, 000 grams
Prevalence of low birthweight births = (number of births with birthweight <2500 grams, or <1, 500 grams, or <1, 000 grams) / (total number of births with birthweight information) Prevalence of high birthweight births = (number of births with birthweight >4, 000 grams) / (total number of births with birthweight information)

These are usually expressed as percent of all livebirths.

Some infants are born too early or too late, and the number of livebirths by gestational age can be used to generate the prevalence of pre-term and post-term births.

The duration of gestation is measured from the first day of the last normal menstrual period. Gestational age is expressed in completed days or completed weeks. Increasingly the use of ultrasonography during prenatal care increases the accuracy of gestational age estimate. While premature infants tend to have low birthweight, gestational age and birthweight are two different concepts, and it is important to distinguish low birthweight due to prematurity and that due to intrauterine growth retardation in a full-term infant.

Pre-term birth = gestational age less than 37 completed weeks

Post-term birth = gestational age of 42 or more completed weeks.

The prevalence is usually expressed as a percent of all livebirths for which gestational age information is available.

Data Sources and Limitations

In calculating rates and proportions, the number of livebirths used in this module of CircHOB may differ from those reported in the fertility module, derived from the various national statistical agencies. In the case of the United States and Canada, these agencies are also the source of information on perinatal deaths, and hence the livebirth counts are identical. For the other jurisdictions, the medical births registry or chief medical officer is used as the source of both the number of livebirths and number of perinatal deaths. The livebirth counts from these sources differ from those of their national statistical agencies in that the birth registries tend to record and report only on births occurring within the country, whereas the national statistical agencies record and report on births to mothers who are citizens/permanent residents regardless of place of delivery. Because of incomplete data capture from health care institutions, the livebirth counts in the medical births registry also tend to be lower than the counts reported by the national statistical agencies.

For the Nordic countries, publications by their medical births registry tend to report birthweight and gestational age data for all births. To obtain birthweight and gestational age data on livebirths only, special requests to the various agencies for custom tabulation is needed.


United States

Counts of late fetal deaths for USA nationally are available from periodic reports in the National Vital Statistics Reports on Fetal and Perinatal Mortality. Data for 2000-2005 can be found in vol 57, no. 8, 2009, the most recently available report. More recent data on early neonatal deaths can be retrieved from the CDC Wonder website on causes of mortality by age. Alaska data are obtained by special request from the Alaska Bureau of Vital Statistics.

Information on birthweight and gestational age of livebirths are available for both USA and Alaska from the National Center for Health Statistics VitalStats website.

Canada

Data on perinatal deaths for Canada and its northern territories are available from Statistics Canada CANSIM Table 102-0508. CANSIM Table 102-4509 provides data on birthweight, while CANSIM Table 102-412 provides data on gestational age.

Greenland

The number of late fetal deaths and distribution of gestational age for Greenland are reported in the annual report of the Chief Medical Officer Årsberetning; the number of perinatal deaths can be calculated from the perinatal mortality rates published in the report. Birthweight data can be found in Statistics Greenland Statbank Table BEELL1.

Faroe Islands

Perinatal mortality data are provided by the Chief Medical Officer in the annual report Sundhedsberetning (called Medicinalberetning before 2006). Birthweight data are reported from 2005 on and gestational age data from 2006 on. 2006-09 data can be found in the 2009 report.

Iceland

Perinatal mortality data are from Statistics Iceland, Table MAN05321. Birthweight data can be found in Table MAN05111.

Gestational age data for the country are reported by the medical births registry at the National Hospital. Data for 2000-09 can be found in Table 2 of the 2010 report Skýrsla frá Fæđingaskráningunni fyrir áriđ 2010.

Denmark

Perinatal mortality data are available from the National Board of Health’s (Sundhedsstyrelsen) Sundhedsdata website. Birthweight data are provided by Statistics Denmark Statbank Table FODV. Gestational age (<37 weeks and 37+ weeks only) can be obtained from the Sundhedsdata website, but breakdown into <37, 37-41, and 42+ are available from annual reports of the medical births registry Fødselsregisteret (foreløbig opgørelse).

Norway

Perinatal mortality data for Norway and its northern regions are available from the website of the Medical Births Registry of the Norwegian Institute of Public Health. Birthweight and gestational age data are by special request.

Sweden

Reproductive health statistics are the responsibility of the Medical Births Registry at the National Board of Health and Welfare (Socialstyrelsen). Due to the change in definition in 2008, the number of perinatal deaths for the 2000-09 period using the 28-week definition for late fetal death was obtained by special request. National and regional data on birthweights and gestational age were also requested from Socialstyrelsen.

Finland

National data on perinatal mortality are available from the publication Parturients, Deliveries and Births 2006, Table 10 for 2000-05 data and Perinatal Statistics 2010, Table 12 for 2006-09 data published by the National Institute for Health and Welfare (THL). Regional data are obtained by special request. National and regional data on birthweights and gestational age are requested from THL.


Russian national and regional data were from the Demographic Yearbook, various years. No data are reported for Taymyr, Evenkia and Koryak AO after 2006.

Data on gestational age of livebirths are not available for Russia nationally or regionally.

Birthweight data for Russia and its regions are reported by the Social Insurance Fund (Fonda socialnogo strahovanija Rossijskoj Federasii ). Registered users can retrieve data from its search and monitoring system (Poiskovo-monitoringovaya sistema). However, the 2500 cut-off point for low-birth weight cannot be used, as it falls between two categories 2000-2399 and 2400-2699, although the proportion of VLBW (<1500 gm) and high birthweight (4000+ gm) are available. CircHOB will report LBW as <2400 gm, Data are available from 2006 on. [/tab] [/tabcontent] [/tabs]