Perinatal Periods of Risk
Practice Collaborative
A CityMatCH, CDC, MCHB/HRSA & March of Dimes Initiative
Methods, Definitions & Recommendations for PPOR Phase 1 Analysis
1. Study population: Live births and infant deaths (both 500 grams or larger birthweight) to resident
mothers using the linked birth and infant death certificate file and fetal deaths (24 weeks or greater
gestational age and 500 grams or larger birthweight) using the fetal death certificate file based on year
of birth. Generally, place of residence at the time of birth defines inclusion in the study no matter
where the place of residence at the time of death. Some communities limit place of residence at both
birth and death.
2. Race/Ethnicity Groups: White non-Hispanic, Black non-Hispanic, Hispanic, American Indian,
Hawaiian, Chinese, Japanese and other. If there is insufficient population size (less than 60 feto-infant
deaths, or less than 10 deaths in any PPOR category) for a specific racial or ethnic group, the group
should not be analyzed separately. Race and ethnicity are based on the race/ethnicity of the mother.
3. Maternal Age Groups: Less than 20 years, and 20 or more years.
4. Maternal Education Groups: 12 years or less, and more than 12 years.
5. Internal Reference Group: Generally, the reference group should be white non-Hispanic, 20 or more
years of age with more than 12 years of education (if more than 60 feto-infant deaths occur among that
population). In addition, a community may want to use some of other meaningful reference group
from within the community or state or some national reference group. When the number of feto-infant
deaths is less than 60, sometime an external reference group can be used instead.
6. Study Variables:

Birthweight: If the birthweight is unknown, its value is imputed based on the gestational age by the
following rule. For infant deaths, gestational ages < 31 weeks are treated as birthweight < 1,500 grams,
and gestational ages < 22 weeks are treated as birthweight birthweight <500 grams. For fetal deaths,
gestational ages < 32 weeks are treated as birthweight < 1,500 grams, and gestational ages < 24 weeks are
treated as birthweight <500 grams. If both birthweight and gestational age are unknown, the death is
excluded from study.
 Gestational age: Gestational age is defined by last menstratual period with unknowns replaced by
clinical estimates. If the gestational age for a fetal death is unknown and the birthweight is known and
500 grams or more, its gestational age is assumed to be of 24 weeks or more gestation.
7. Data Quality:

Places with greater than 10% missing of both birthweight and gestational age in fetal, infant or
combined deaths, and places with greater than 10% imputed birthweight and/or gestational age have a
major data quality issue. Caution is strongly recommended when using PPOR approach. Because the
actual feto-infant mortality rates are underestimates.

Places with greater than 10% unknown for some of maternal race/ethnicity, age and education
variables, also have a major data quality issue. In order not to introduce bias, it is important to define the
target/reference populations using other variables or use external reference groups.
8. Number of Events: Populations with fewer than 60 feto-infant deaths (or with less than 10 deaths in
any of the four PPOR categories) experience substantial instability estimating their PPOR rates and it
is difficult to accurately interpret the PPOR findings. The PPOR approach may not be the best
approach for studying such populations.
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