Background:Newborns of 30-34 weeks gestation comprise 3.9%of all live births in the United States and 32%of all premature infants. They have been studied much less than very low birthweight infants. Objective:To measure in-hospital outcomes and readmission within three months of discharge of moderately premature infants. Design:Prospective cohort study including retrospective chart review and telephone interviews after discharge. Setting:Ten birth hospitals in California and Massachusetts. Patients:Surviving moderately premature infants born between October 2001 and February 2003.Main outcome measures:(a) Occurrence of assisted ventilation during the hospital stay after birth; (b) adverse in-hospital outcomes-for example,necrotising enterocolitis; (c) readmission within three months of discharge. Results:With the use of prospective cluster sampling,850 eligible infants and their families were identified,randomly selected,and enrolled. A total of 677 families completed a telephone interview three months after hospital discharge. During the birth stay,these babies experienced substantial morbidity:45.7%experienced assisted ventilation,and 3.2%still required supplemental oxygen at 36 weeks. Readmission within three months occurred in 11.2%of the cohort and was higher among male infants and those with chronic lung disease. Conclusions:Moderately premature infants experience significant morbidity,as evidenced by high rates of assisted ventilation,use of oxygen at 36 weeks,and readmission. Such morbidity deserves more research. Background: Newborns of 30-34 weeks gestation comprise 3.9% of all live births in the United States and 32% of all premature infants. They have been studied much less than very low birthweight infants. Objective: To measure in-hospital outcomes and readmission Design: Prospective cohort study including retrospective chart review and telephone interviews after discharge. Settings: Ten birth hospitals in California and Massachusetts. Patients: Surviving moderately premature infants born between October 2001 and February 2003. Main (a) Occurrence of assisted ventilation during the hospital stay after birth; (b) adverse in-hospital outcomes-for example, necrotising enterocolitis; (c) readmission within three months of discharge. Results: With the use of prospective cluster sampling, 850 eligible infants and their families were identified, randomly selected, and enrolled. A total of 677 families completed a telephone inter During the birth stay, these babies have experienced substantial morbidity: 45.7% experienced assisted ventilation, and 3.2% still required supplemental oxygen at 36 weeks. Readmission within 3 months occurred in 11.2% of the cohort and was higher among male infants and those with chronic lung disease. Conclusions: Moderately premature infants experience significant morbidity, as evidenced by high rates of assisted ventilation, use of oxygen at 36 weeks, and readmission. Such morbidity deserves more research.