Factors affecting the incidence of chronic lung disease of prematurity in 1987, 1992, and 1997

Objective-To determine changes in the incidence of chronic lung disease of prematurity between 1987, 1992, and 1997. Methods-Observational study based on data derived from a geographically defined population: Trent Health Reg ion, United Kingdom. Three time periods were compared: I February 1987 to 3 1 January 1988 (referred to as 1987); 1 April 1992 to 31 March 1993 (referr ed to as 1992); 1997. Ah infants of less than or equal to 32 completed week s gestation born to Trent resident mothers within the study periods and adm itted to a neonatal unit were included. Rates of chronic lung disease were determined using two definitions: (a) infants who remained dependent on act ive respiratory support or increased oxygen at 28 days of age; (b) infants who remained dependent on active respiratory support or increased oxygen at a corrected age of 36 weeks gestation. Results Between 1987 and 1992 there was a fall in the birth rate, but a sig nificant increase was noted in the number of babies of less than or equal t o 32 weeks gestation admitted to a neonatal unit. There was no significant change in survival when the two groups of infants were directly compared. H owever, mean gestation and birth weight fell. Adjusting for this change sho wed a significant improvement in survival (28 day survival: odds ratio (OR) = 1.69; 95% confidence interval (95% CI)= 1.23 to 2.33. Survival to 36 week corrected gestation: OR = 1.45; 95% CI = 1.06 to 1.98). These changes were accompanied by a large increase in the incidence of chronic lung disease e ven after allowing for the change in population characteristics (28 day def inition: OR = 2.20; 95% CI = 1.47 to 3.30. 36 week definition: OR = 3.04; 9 5% CI = 1.91 to 4.83). Between 1992 and 1997 a different pattern emerged. T here was a further increase in the number of babies admitted for neonatal c are at less than or equal to 32 weeks gestation despite a continuing fall i n overall birth rate. Survival, using both raw data and data corrected for changes in gestation and birth weight, improved significantly in 1997 (adju sted data: 28 day survival: OR = 1.72 (95% CI = 1.22 to 2.38); survival to 36 week corrected gestation: OR = 1.90 (95% CI = 1.36 to 2.64)). Rates of c hronic lung disease showed no significant change between 1992 and 1997 desp ite improved survival (adjusted data: 28 day definition: OR = 0.72 (95% CI = 0.50 to 1.03); 36 week definition: OR = 0.88 (95% CI = 0.61 to 1.26). Conclusions-Current high rates of chronic lung disease are the result of po licies to offer neonatal intensive care more widely to the most immature in fants. Recent improvements in survival have been achieved without further i ncreases in the risk of infants developing chronic lung disease.