Relation between size of delivery unit and neonatal death in low risk deliveries: population based study.

AIM To examine risk of neonatal death after low risk pregnancies in relation to size of delivery units. METHODS A population based study of live born singleton infants in Norway with birthweights of at least 2500 g was carried out. Antenatal risk factors were adjusted for. RESULTS From 1972 to 1995, 1.25 million births fulfilled the criteria. The neonatal death rate was lowest for maternity units with 2001-3000 annual births and steadily increased with decreasing size of the maternity unit to around twice that for units with less than 100 births a year (odds ratio 2.1; 95 % confidence interval 1.6 to 2.8). Institutions with more than 3000 deliveries a year also had a higher rate (odds ratio 1.7; 95% CI 1.4 to 2.0), but analyses suggest that this rate is overestimated. CONCLUSION Around 2000 to 3000 annual births are needed to reduce the risk of neonatal deaths after low risk deliveries.