Life-table analysis of the risk of perinatal death at term and post term in singleton pregnancies

OBJECTIVE: This study was undertaken to estimate the cumulative risk of per inatal death associated with delivery at each gestational week both at term and post term. STUDY DESIGN: The numbers of antepartum stillbirths. intrapartum stillbirth s, neonatal deaths, and surviving neonates delivered at between 37 and 43 w eeks' gestation in Scotland, 1985-1996, were obtained from national databas es (n = 700,878) after exclusion of multiple pregnancies and deaths caused by congenital abnormality. The numbers of deaths at each gestational week w ere related to appropriate denominators: antepartum stillbirths were relate d to ongoing pregnancies, intrapartum stillbirths were related to all birth s (excluding antepartum stillbirths), and neonatal deaths were related to l ive births. The cumulative probability of perinatal death associated with d elivery at each gestational week was estimated by means of life-table analy sis. RESULTS: The gestational week of delivery associated with the lowest cumula tive risk of perinatal death was 38 weeks' gestation, whereas the perinatal mortality rate was lowest at 41 weeks' gestation. The risk of death increa sed more sharply among primigravid women after 38 weeks' gestation because of a greater risk of antepartum stillbirth. The relationships between risk of death and gestational age were similar for the periods 1985-1990 and 199 1-1996. CONCLUSION: Delivery at 38 weeks' gestation was associated with the lowest risk of perinatal death.