Аннотация:Despite the enormous effort of many investigators, a variety of problems have made it difficult to assess the long-term outcome of extremely low-birth-weight (ELBW [<1000 g]) infants in a valid, meaningful, and useful manner. For example, partly because of limited support, most follow-up programs have included only the ELBW infants discharged from a specific center, including maternal and neonatal referrals, thus potentially introducing selection bias. Ideally, all ELBW infants born to residents of a defined geographic region should be evaluated. In addition, loss of 20% to 30% of infants to follow-up might substantially bias the observed rate of handicap because the lost infants may not be representative of the whole group. Such loss is difficult to avoid in following high-risk populations for more than a few years after birth. It is also important to assure that the assessment of preterm infants is not affected by examiner expectations or biases; therefore,
