Respiratory morbidities/mortality within 2 years in BPD patients
From 2002 to 2015, 69,245 patients (0.95% of total live births in Korea) were diagnosed with RDS (P22.0). After applying the exclusion criteria, 55066 patients (79.5%) were finally included in the analysis (Supplementary Figure S1), 9470 (17.2%) of whom were diagnosed with BPD. Perinatal co-morbidities including surgically treated patent ductus arteriosus, intraventricular hemorrhage, pulmonary hypertension, necrotizing enterocolitis, retinopathy of prematurity, and neonatal sepsis were significantly higher in the BPD group than the non-BPD group (P<.001, Table 1). Rehospitalization for LRI within 2 years of birth occurred in 53.9% of BPD patients and 37.9% of non-BPD patients (P<.001, Table 1).
Among readmitted patients, the median number of readmissions within 2 years of birth was twice as high in the BPD group than the non-BPD group (2 (1–40) vs. 1 (1–29), P<.001, Table 2). Patients in the BPD group showed a significantly longer hospital stay and higher rates of mechanical ventilator, non-invasive ventilator, and oxygen use than those in the non-BPD group (14.9% vs. 2.7%, 3.9% vs. 0.5%, and 41.0% vs. 14.5%, respectively, P<.001, Table 2). Furthermore, compared with those in the non-BPD group, patients in the BPD group were 4.7 times more likely to require ICU care and stayed in the ICU 2.4 times longer (P<.001, Table 2).
The relative risk (RR) of BPD on readmission because of LRI significantly and steadily increased from 2002 to 2015 (1.42, 95% confidence interval [CI], 1.39–1.45, Figure 1A). The RR of BPD on ICU admission was much higher than that on total readmission (6.53, 95% CI, 5.96–7.15, Figure 1B). The RRs of both total readmission and ICU admission showed an increasing trend between 2005 and 2006; the RR of ICU admission peaked in 2010 (8.60, 95% CI, 6.32–11.70, Figure 1).
Of the 55066 patients, 651 (1.18%) died within 2 years. The mortality rate was significantly higher in the BPD group than the non-BPD group (2.8% vs. 0.8%, P<.001, Table 1). Respiratory morbidity caused 42.4% and 25.3% of deaths in the BPD and non-BPD groups, respectively (P<.001, Supplementary Table S8).
Respiratory morbidities in VLBW infants
Of the total population, 33437 patients (60.7%) were included in a subgroup analysis based on birth weight of <1,500 g or >1,500 g. BPD was diagnosed in 58.7% and 7.2% of the <1,500 g and >1,500 g groups, respectively. Compared with the non-BPD group, the BPD group had a significantly higher readmission frequency; more days in the hospital; and higher mechanical ventilator, non-invasive ventilator, and oxygen use on readmission within 2 years in both the <1,500 g and >1,500 g birth weight subgroups. The number of ICU admissions was not higher in patients with BPD in the >1,500 g group (Supplementary Table S9).
Patients with BPD showed similar RRs for readmission because of LRI in both the <1,500 g (1.23, 95% CI: 1.17–1.29, Supplementary Figure S2) and >1,500 g groups (1.28, 95% CI: 1.22–1.34). All patients with RDS born between 2011 and 2015 had an RR for readmission of 1.36 (Supplementary Figure S2).
Asthma prevalence and asthma-related morbidities in BPD
Patients born between 2002 and 2012 were included in the analysis. Of 33,129 children, asthma prevalence at ages 3 and 5 was 49.7% and 38.7%, respectively. The proportion of patients diagnosed with asthma was significantly higher in the BPD group than the non-BPD group at both ages 3 (57.6% vs. 48.9%, P<.001) and 5 (44.3% vs. 38.2%, P<.001). Total asthma prevalence decreased at age 5 (Table 3). The number of hospital admissions for asthma and the duration of hospitalization among admitted patients were higher in the BPD group than in the non-BPD group (Table 3). The RR of BPD on asthma diagnosis was 1.06–1.37 at age 3 and 1.05–1.23 at age 5 (Figure 2).