RESUMEN
<p><b>OBJECTIVE</b>To understand the risk factors for respiratory distress syndrome (RDS) by comparing the perinatal conditions of preterm infants with different severities of RDS.</p><p><b>METHODS</b>A total of 667 preterm infants with RDS were classified into 4 groups according to the chest X-ray severity: grade I (217 cases), grade II (225 cases), grade III (126 cases) and grade IV (99 cases). The perinatal conditions of the preterm infants were reviewed retrospectively.</p><p><b>RESULTS</b>There were no significant differences in the gender, the percentage of twins, the percentage of the younger one in twins, maternal age, the percentage of using antenatal corticosteroids, the percentage of premature rupture of membranes, the percentage of placental abruption, the delivery mode and the fertilization mode in preterm infants with different severities of RDS. With the increasing severity of RDS, the birth weight and the gestational age decreased, and the percentage of the infants with Apgar score ≤7 or maternal pregnancy-induced hypertension increased (P<0.05).</p><p><b>CONCLUSIONS</b>The severity of RDS is related to gestational age, birth weight and perinatal asphyxia in preterm infants.</p>