title: Survival estimations at the limit of viability.
abstract: 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.
authors.affiliation: a Neonatology Division, Gregorio Marañon University Hospital, Biomedical Research Institute Gregorio Marañon, Complutense University , Madrid , Spain.
authors.forename: Susana
authors.initials: S
authors.lastname: Zeballos-Sarrato
authors.affiliation: a Neonatology Division, Gregorio Marañon University Hospital, Biomedical Research Institute Gregorio Marañon, Complutense University , Madrid , Spain.
authors.forename: Sonia
authors.initials: S
authors.lastname: Villar-Castro
authors.affiliation: a Neonatology Division, Gregorio Marañon University Hospital, Biomedical Research Institute Gregorio Marañon, Complutense University , Madrid , Spain.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Zeballos-Sarrato
authors.affiliation: a Neonatology Division, Gregorio Marañon University Hospital, Biomedical Research Institute Gregorio Marañon, Complutense University , Madrid , Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Ramos-Navarro
authors.affiliation: a Neonatology Division, Gregorio Marañon University Hospital, Biomedical Research Institute Gregorio Marañon, Complutense University , Madrid , Spain.
authors.forename: Noelia
authors.initials: N
authors.lastname: González-Pacheco
authors.affiliation: a Neonatology Division, Gregorio Marañon University Hospital, Biomedical Research Institute Gregorio Marañon, Complutense University , Madrid , Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Sánchez Luna
mesh_terms: D046689:Fetal Mortality; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D007231:Infant, Newborn; D007234:Infant, Premature; D007363:Intensive Care Units, Neonatal; D013030:Spain / Q000453:epidemiology; D015996:Survival Rate
keywords: Foetal mortality; infant; perinatal mortality; premature; premature birth; survival rate