Prolonged pregnancy poses a number of risks to the fetus including meconium aspiration, birth injury and hypoxia. However, the concern that most occupies the minds of mothers and medical attendants, is the risk of fetal loss. Gestation-specific stillbirth rates expressed per 1000 total births at each week of gestation, is often incorrectly interpreted as equating to risk of stillbirth. As only women who are still pregnant are at risk of stillbirth, it would be more appropriate to calculate the risk of stillbirth as a proportion of the ongoing pregnancies at a particular gestation1. By contrast, it is appropriate to use the number of live births as the denominator for neonatal mortality, as a neonate is at risk of dying only after it is liveborn. Most major studies on gestation-specific perinatal mortality were carried out before modern advances in the accuracy of determining gestational age1–5. Additionally, late neonatal and post-neonatal deaths are excluded from most analyses of obstetric outcome, even though preterm and post-term delivery has been associated with an increased risk of infant loss for up to two years6.
The aim of this study was to evaluate the rates of stillbirth and infant mortality per 1000 total or live births and ongoing pregnancies at each given gestation. The former allows direct comparison with other published studies, while the latter is a better reflection of mortality risk faced by the fetus and infant at each week of gestation. For this purpose we examined a large regional database of birth notifications linked to stillbirth and infant death registration.