Risk factors for respiratory distress syndrome in the newborn. A multicenter Italian survey. Study Group for Lung Maturity of the Italian Society of Perinatal Medicine

Risk factors for respiratory distress syndrome (RDS) in the newborn have been evaluated using data from a large survey conducted between 1980 and 1989 in selected periods in eleven perinatal units placed in five Italian regions. A total of 1624 liveborn infants consecutively delivered at the collaborating centers, at delivery 26-37 weeks gestational age and without clinically evident congenital anomalies were included in the survey. All the newborns were followed up to the 28th day of life. A total of 131 newborns (7.8%) developed RDS. Overall 1st-7th and 1st-28th day of life infant mortality rates were 54.8 and 61.6/1,000 livebirths; the corresponding rates in babies who developed RDS were 419.8 and 465.6/1,000 livebirths. The frequency of RDS was higher in males than in females and the corresponding relative risk, RR, was 0.7, with 95% confidence interval, CI, ranging from 0.5 to 0.9. The risk of RDS markedly increased with decreasing birth weight: compared to babies weighing more than 2500 g at birth the RR estimates were respectively 1.4, 4.5, 8.8 and 39.3 in those weighing >2000-2500 g, >1500-2000 g, >1000-1500 g and 1000 g or less. Likewise, compared to babies born between the 35th and the 37th week of gestation, the RR of RDS was 3.3 and 21.5 in those born between the 31st-34th or before the 31st week of gestation. Multiple pregnancy, gestational or chronic diabetes, pregnancy-induced or chronic hypertension and premature rupture of the membranes were not related to the risk of RDS. Smoking in pregnancy was reported by five mothers among cases with RDS (3.8%) and 83 among those who did not develop the disease (9.3%): the corresponding RR was 0.4 with 95% CI ranging from 0.2 to 0.9. Compared to vaginal births, babies delivered by intrapartum cesarean section had an increased risk of RDS (RR 1.8, 95% CI from 1.2 to 2.7), but babies delivered by elective cesarean section were at not significantly decreased risk (RR 0.5, 95% CI 0.3 to 1.1). Low Apgar score at 1st and 5th minute (less than 7) was associated with an increased risk of RDS, the RR estimates being, compared to babies with Apgar score equal to 7 or more, 7.9 at 1 minute of age and 8.4 for 5 minutes of age.