The Mortality of Periviable and Extremely Premature Infants and Their Impact on the Overall Neonatal Mortality Rate.

To investigate mortality in periviable neonates ≤23 weeks gestational age and calculate its impact on overall neonatal mortality rate over a 12-year period (1998-2009). Verify if periviable mortality decreased in the period (2010-2015). Retrospective review.