Definition: In this task, you are given an abstract of article. Your task is to generate title for this article. Preferred titles are under thirty words.
Input: CONTEXT Although cerebral palsy (CP) among extremely premature infants has been reported as a major morbidity outcome, there are difficulties comparing published CP rates from many sites over various birth years.   
 OBJECTIVE To assess the changes in population-based, gestational age-specific prevalence rates of CP among extremely premature infants over 30 years.   
 DESIGN Prospective population-based longitudinal outcome study.   
 SETTING AND PARTICIPANTS In Northern Alberta, 2318 infants 20 to 27 weeks' gestational age with birth weights of 500 to 1249 g were liveborn from 1974 through 2003. By 2 years of age, 1437 (62%) had died, 23 (1%) were lost to follow-up, and 858 (37%) had received multidisciplinary neurodevelopmental assessment.   
 MAIN OUTCOME MEASURE Population-based prevalence rates of CP were determined. Logistic regression with linear spline was used to assess changes in CP prevalence over time.   
 RESULTS At age 2 years, 122 (14.2%) of 858 survivors had CP. This diagnosis was confirmed for each child by age 3 years or older. Among those whose gestational age was 20 to 25 weeks, population-based survival increased from 4% to 31% (P<.001), while CP prevalence per 1000 live births increased monotonically from 0 to 110 until the years 1992-1994 (P<.001) and decreased thereafter to 22 in the years 2001-2003 (P<.001). Among those whose gestational age was 26 to 27 weeks, population-based survival increased from 23% to between 75% and 80% (P<.001), while CP prevalence per 1000 live births increased monotonically from 15 to 155 until the years 1992-1994 (P<.001) and then decreased to 16 in the years 2001-2003 (P<.001). For all survivors born in the years 2001-2003, CP prevalence was 19 per 1000 live births.   
 CONCLUSION Population-based CP prevalence rates for children whose gestational age was 20 to 27 weeks and whose birth weight ranged from 500 to 1249 g show steady reductions in the last decade with stable or reducing mortality, reversing trends prior to 1992-1994.

Changes in the prevalence of cerebral palsy for children born very prematurely within a population-based program over 30 years.