Late preterm babies have important morbidity when compared with term babies, with oxygen requirement and more days of hospitalization. If antenatal corticosteroid therapy is necessary for fetal lung maturation after 34 weeks, it remains to be established. The systematic review with metanalysis in Cochrane Library includes a small number of late preterm babies and no conclusion about effectiveness of corticoid therapy in this setting could be drawn. Our hypothesis is that antenatal corticosteroid therapy is effective to prevent respiratory disease and morbidity in late preterm babies and this study will be carried out to evaluate this question.