From December @ to March @ , @ preterm infants with RDS who received intubation-pulmonary surfactant ( PS ) - extubation in our NICU were randomly divided ( by means of random number table ) into three groups based on the primary mode of ventilation : nasal continuous positive airway pressure -LSB- NCPAP , n = @ , male/female ratio was @/@ , mean gestational age ( GA ) was ( @ @ ) weeks , mean birth weight ( BW ) was ( @ @ ) g -RSB- , bi-level positive airway pressure -LSB- BiPAP , n = @ , male/female ratio was @/@ , GA was ( @ @ ) weeks , BW was ( @ @ ) g -RSB- , and synchronized bi-level positive airway pressure -LSB- SBiPAP , n = @ , male/female rate was @/@ , GA was ( @ @ ) weeks , BW was ( @ @ ) g -RSB- .