The recorded neonatal data were gestational age at birth; birth weight; body length and head circumference; gender; singleton pregnancy; Apgar scores at 1′ and 5′; the need of tube feeding at discharge. The parameters recorded at 36 weeks of gestational age were the severity of bronchopulmonary dysplasia; the presence of post-natal growth retardation; body weight and length, and head circumference. The medications recorded included pre- and post-natal steroids, artificial surfactants and diuretics. A record was also made of the occurrence of patent ductus arteriosus, surgical necrotising enterocolitis, intraventricular hemorrhage, retinopathy of prematurity and sepsis, defined as the presence of a positive blood culture. Respiratory support was recorded as the number of days of assisted ventilation and the number of days of supplemental oxygen therapy at an FiO2 value >0.21.