Background Postnatal care and growth in extremely low birth weight (ELBW) infants are being increasingly focused on worldwide. However, few data from China have been reported, expecially multicenters. This multicenter study was designed to investigate the problems existing in postnatal care, weight gain and the related risk factors in in-patient ELBW infants. Methods Eligible ELBW infants admitted to involved neonatal intensive care units (NICUs) in 2017 in Beijing were studied retrospectively. Except for general early outcomes, Weight Z score and feeding practice related information was caculated, and collected. Growth retardation (GR) was diagnosed if body weight Z score at discharge dropped more than one standard deviation (SD) compared with birth. Results Of our cohort of 137 ELBW infants, 92 infants discharged with medical advice were analyzed. Full enteral feeding reached at 37.0 (27.0, 51.8)days. Exclusive breast milk feeding rate was 30.4% at discharge. All infants had decreased weight Z score, and its change was similar in different weight subgroups. The incidence of GR was 66.3%. Multiple-factor analysis showed the risk factors for GR were small for gestational age(OR 34.768, 95%CI 1.652-731.728), average weight gain rate 28days(OR 6.867, 95%CI 1.211–38.957), P༜0.05. Keeping ELBW infants staying in hospital longer was beneficial to their weight gain (OR = 0.950, 95% CI 0.909–0.993, P
