Studies in Fetal and Infant Mortality. I. A Methodological Approach to the Definition of Perinatal Mortality

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Abstract
A bird''s eye view of the interplay between biological and environmental factors of mortality during the 1st year of life is described. Mortality at ages where biological factors are the more important (typically neonatal mortality as opposed to postneonatal mortality) is characterized by: greater sex differences and less racial differences, smaller variability, weaker correlation with the level of living, and less reduction with the improvement of the environment by time. Applying the same approaches after dividing the 1st year into finer age groups provides a method for a method for a better definition of the upper limit to the perinatal period, where perinatal mortailty is mean to be a measure of mortality due to prenatal and natal (or biological) factors. The point of time during the first year of life at which there is a tendency of reversal of the fore-mentioned characteristics can be taken as the upper limit to the perinatal period. The results show that the neonatal period as currently defined is not a homogeneous one. Until we have a better knowledge of the actual caused of fetal and infant loss, the term perinatal mortality should, preferably, be limited to include deaths during the 1st week, or 2nd at most, beside the fetal deaths.