Related to Infant Mortality, Perinatal Mortality is a measure of the number of deaths of babies from viability until a certain number of days after birth. The CDC recognized 2 definitions. The first, includes fetal and infant deaths from 28 weeks gestation, until 7 days after birth. This definition is useful for comparing international populations since deaths from 20-27 weeks gestation are not reported in the same ways worldwide. The second definition, which is preferred in the United States, is any death from 20 weeks gestational age to 28 days after birth. That definition is thought to more thoroughly assess perinatal mortality in a population because of the large number of fetal deaths that happen between 20 and 28 weeks gestation. An easy way to remember what perinatal mortality is would be the number of stillbirths plus the number of neonatal deaths in a given population. The difference between Perinatal Mortality and Infant Mortality is that Perinatal Mortality is defined as a distinct period of time, making it easier to compare the Perinatal Mortality Rate of any two populations.
When used in statistics, perinatal mortality is expressed as a rate (Perinatal Mortality Rate, or PMR), which is the number of perinatal deaths per 1,000 live births in a given year. The term is used in both medicine and social sciences, and is widely considered to be a useful way of evaluating the quality of prenatal and neonatal care.
The World Health Organization has not published data on perinatal mortality since 2000. The data available from that report shows a major discrepancy between the developed world and the undeveloped world, where the PNR is as much as 80 times higher.
Perinatal Mortality Rate can be useful to compare populations that use different definitions for Infant Mortality. In particular, the United States fares better as compared to other developed nations when PNR is used for comparison, rather than IMR (Infant Mortality Rate).