Population-based study of bronchopulmonary dysplasia in very low birth weight infants in Switzerland

In Switzerland, data are collected prospectively by collaborators from all nine neonatal intensive care units and their affiliated paediatric units caring for neonates, to determine survival and (pulmonary) outcome of infants with birth weights ranging from 501 to 1500 g. To assess the pulmonary outcome of very low birth weight (VLBW) infants in Switzerland in 1996 and 2000, factors associated with bronchopulmonary dysplasia (BPD) were identified and compared with pulmonary outcomes from the Vermont Oxford Network data. BPD was defined as a requirement for supplemental oxygen at 36 weeks postmenstrual age. Complete data were available for 600 and 636 VLBW infants in 1996 and in 2000, respectively. Mortality rates in Switzerland were significantly higher (1996: 19.2%, 2000: 20.8%) than in the Vermont Oxford Network (1996: 14%, 2000: 14%). Expressed as percentage of infants still hospitalised at 36 weeks postmenstrual age, 16.7% and 13.2% of Swiss VLBW infants were diagnosed with BPD in 1996 and 2000, respectively. These rates were significantly lower than in the Vermont Oxford Network (1996: 28%, 2000: 35%). Infants exposed to factors previously shown to be associated with BPD were investigated: in Switzerland, infants with a history of surfactant replacement therapy and/or mechanical ventilation had a significantly higher rate of BPD in both cohorts. Infants with postnatal transport, sepsis proven by positive blood culture and patent ductus arteriosus had a higher BPD rate only in the 1996 cohort. Between 1996 and 2000, mortality rates and incidence of BPD in VLBW infants remained unchanged in Switzerland. BPD rates in Switzerland are lower than those found in the Vermont Oxford Network whereas a mortality rate comparison displays an inverted picture. We suspect that these effects are interrelated and may be due in part to a selective approach of Swiss neonatologists to resuscitation of infants in the smallest birth weight stratum.

The factors listed above have apparently become less important in the context of bronchopulmonary dysplasia and other influences, including prenatal conditions, will need to be investigated.