Risk Factors in Bronchopulmonary Dysplasia (Newborn Lung Project)

BACKGROUND:

Despite many improvements in neonatal intensive care during the decade from 1977 to 1987, infant respiratory distress syndrome remained a major public health problem. Increasing survival among premature infants led to the emergence of BPD as the major chronic respiratory disorder of infancy. The vast majority of BPD occurs in very low birth weight infants weighing less than 1,500 grams.

Although the incidence of low birth weight births declined from 1977 to 1987, the rate of very low birth weight births remained unchanged. These infants had a relative risk of neonatal death almost 200 times greater than full-term infants. Among survivors, eight percent had evidence of chronic pulmonary disease at forty weeks of age. The Institute of Medicine reported that very low birth weight infants who survived to one year of age were hospitalized for an average of 57 days after birth versus 3.5 days for full-term infants. Up to forty percent of these infants would be re-hospitalized almost two times for an average of 16 days versus 8.7 percent of normal birth weight infants for an average of 8 days.

DESIGN NARRATIVE:

The study had a nested case-control design. In the first year of the project, the diagnosis of BPD was standardized and a scoring system developed for grading the severity of the disease. Baseline data were collected on very low birth weight neonates admitted to seven participating neonatal intensive care units. Maternal interviews were conducted for neonates surviving seven days. The purpose of the interview was to collect information which m;ight be related to a predisposition to BPD, respiratory distress syndrome, or prematurity. Specific areas addressed included familial diseases in general and respiratory diseases in particular, familial patterns of prematurity, pregnancy and birth history, circumstances surrounding delivery, environmental exposures, health habits such as smoking, and socioeconomic variables. Severity scoring and diagnosis of the infants were based on the hospital log and routine x-rays. Final analysis compared infants with BPD to those without BPD, controlling for confounders and placing special emphasis on interaction effects. Full-term neonates served as controls.