New Australian birthweight centiles

Objectives: To prepare more accurate population-based Australian birthweight centile charts by using the most recent population data available and by excluding pre-term deliveries by obstetric intervention of small for gestational age babies. Design: Population-based retrospective observational study. Setting: Australian Institute of Health and Welfare National Perinatal Data Collection. Participants: All singleton births in Australia of 23–42 completed weeks’ gestation and with spontaneous onset of labour, 2004–2013. Births initiated by obstetric intervention were excluded to minimise the influence of decisions to deliver small for gestational age babies before term. Main outcome measures: Birthweight centile curves, by gestational age and sex. Results: Gestational age, birthweight, sex, and labour onset data were available for 2Â 807Â 051 singleton live births; onset of labour was spontaneous for 1Â 582Â 137 births (56.4%). At pre-term gestational ages, the 10th centile was higher than the corresponding centile in previous Australian birthweight charts based upon all births. Conclusion: Current birthweight centile charts probably underestimate the incidence of intra-uterine growth restriction because obstetric interventions for delivering pre-term small for gestational age babies depress the curves at earlier gestational ages. Our curves circumvent this problem by excluding intervention-initiated births; they also incorporate more recent population data. These updated centile curves could facilitate more accurate diagnosis of small for gestational age babies in Australia