The aim of this study is to model longitudinal data at NICU of Assuit University Children Hospital to create predictive growth charts for weight in preterm infants from birth till discharge, that take into account the differing growth rates post-birth when compared to in-utero growth ,and to compare it with WHO chart for preterms.

It is an observational retrospective study achieved by collecting retrospective, longitudinal measurements of weight from preterm infants born at <34 weeks gestation, starting from birth, and model gender- and gestation specific predictive centile charts till discharge from the neonatal unit by a population-based cohort study.

Inclusion Criteria:

• Data will be collected for all infants born at <34 weeks of gestation who were delivered by vaginal or caesarian section and born at Assuit University Hospital or referred to it.

Exclusion Criteria:

• (1) Any neonate born at 34 weeks of gestation or more, (2) any neonate born at <34 weeks of gestation who died before a second weight could be recorded.

we will compare the difference of weight gain between males and females infants

It is an observational retrospective study achieved by collecting retrospective, longitudinal measurements of weight from preterm infants born at <34 weeks gestation, starting from birth, and model gender- and gestation specific predictive centile charts till discharge from the neonatal unit by a population-based cohort study.