Neurodevelopmental Disabilities

Among the earliest concerns about the health of premature infants was the association between preterm delivery and neurodevelopmental disabilities. Neurodevelopmental disabilities are a group of chronic interrelated disorders of central nervous system function due to malformation of or injury to the developing brain. The spectrum of neurodevelopmental disabilities includes the major disabilities: cerebral palsy (CP) and mental retardation. Sensory impairments include visual impairment and hearing impairment. The more subtle disorders of central nervous system function include language disorders, learning disabilities, attention deficit-hyperactivity disorder (ADHD), minor neuromotor dysfunction or developmental coordination disorders, behavioral problems, and social-emotional difficulties.

Early studies focused primarily on cognitive impairment, as measured by intelligence quotient (IQ) and by the detection of motor abnormalities on standardized neurological examinations. A landmark study, the Collaborative Perinatal Project of the National Institute of Neurological and Communicative Disorders and Stroke, monitored 35,000 children born before neonatal intensive care (i.e., in the late 1950s and early 1960s) for 7 years. Although only 177 children born at less than 34 weeks gestation survived, the study documented the increased risk of cognitive and motor impairment as a function of decreasing gestational age (Hack et al., 1993; McCormick et al., 1980). It highlighted the need for neurodevelopmental follow-up of populations born preterm, especially as the emergence of neonatal intensive care and high-risk obstetric care dramatically reduced gestational age-specific mortality rates but not preterm birth rates (see Chapters 1, 2, and 10). The history of neonatal intensive care is not only one of miracles achieved, but also of therapeutic misadventures (Allen, 2002; Baker, 2000; Silverman, 1980; Silverman, 1998). Iatrogenic complications have contributed to adverse health and neurodevel-opmental outcomes in the past, but a shift from a trial and error approach toward evidence based medicine is establishing a more empiric basis for treating mothers and preterm infants. Although new therapies are generally evaluated in randomized clinical trials, the safety and efficacy of many currently used treatments and medications have not been adequately studied (see Chapter 10).

The resulting literature demonstrates wide variations in the prevalence of neurodevelop-mental disabilities (Allen, 2002; Aylward, 2002; Aylward, 2002a; Aylward, 2005). Much of this variation is due to methodological issues, for example, a lack of uniformity in sample selection criteria, the method and the length of follow-up, follow-up rates, and the outcome measures and the diagnostic criteria used. Variations in outcome frequencies reported also reflect differences in the population base and in clinical practice. Whenever possible, outcomes data are provided by gestational age categories for preterm infants born in the 1990s to the present. However, because the age of evaluation determines which outcomes can be assessed, recent studies of the outcomes for adolescents who were born preterm report on preterm births that occurred in the 1980s. The time lag required for followup makes caution necessary in generalizing reported adolescent and adult outcomes to preterm infants who survive with the technology available today. Perinatal and neonatal risk factors do not reliably predict these long-term outcomes. Therefore, research is needed to identify better neonatal predictors of neurodevelopmental disabilities, functional abilities, health and other long-term outcomes.

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