Survival estimations at the limit of viability.

Objective: The purpose of this study was to assess the variability in neonatal survival to discharge from the neonatal unit by using different inclusion criteria.

Methods: An observational and descriptive study was performed between January 2008 and December 2013 which included infants born between 22 weeks and 31 weeks and 6 d of gestation. The rate of survival was calculated using three different inclusion criteria: the total number of preterm births, the number of all preterm live births, and the number of preterm newborns admitted to the neonatal unit.

Results: A total of 783 patients met the inclusion criteria. The survival rate for births between 22 and 31 weeks and 6 d of gestation was 72.8% of total births, 82.3% of live births, and 84.0% of all admissions to the neonatal unit. Therefore, we found a significant difference in survival rates according to whether or not foetal mortality (11.6%) and mortality in the delivery room (2.0%) were included. This variation increased with decreasing gestational age: 17,2%, 25%, and 38,4% at 23 weeks gestation.

Conclusions: Late foetal mortality and the mortality in the delivery room affect the survival rates of preterm infants significantly, especially the most immature newborns.