Incidence-based measures of birth, growth restriction, and death can free perinatal epidemiology from erroneous concepts of risk.

BACKGROUND: Traditional perinatal epidemiology appears to embrace fallacious concepts of risk. The use of incorrect denominators for perinatal rates is commonplace both for straightforward indices such as the gestational age-specific labor induction rate and also for the more conceptually challenging indices such as the gestational age-specific neonatal mortality rate. As a consequence, perinatology is beset by several conondrums including the paradox of intersecting perinatal mortality curves. PROPOSITION: These traditions are ideally replaced by alternative concepts that may be derived a priori and measured using indices such as presented here: the incidence of birth (i.e., the gestational age-specific birth rate), the incidence of growth restriction (i.e., the gestational age-specific growth-restriction rate) and the incidence of death (i.e., the age-specific mortality rate).

RESULTS: The incidence of birth, growth restriction, and death quantify the core phenomena in perinatology and reveal congruent and coherent patterns of occurrence.

CONCLUSIONS: These new indices can free perinatal epidemiology from erroneous concepts of risk and resolve the paradoxal phenomena that plague the perinatal domain. They also permit the development of a theoretical framework for obstetric intervention, which in recent years has been based exclusively on empirical evidence.