Australian national birthweight percentiles by gestational age

Objective: To develop national birthweight: percentiles by gestational age for male and female singleton infants born in Australia, and to compare the birthweight percentiles of Indigenous and non-indigenous infants. Design and setting: Cross-sectional study of singleton live births to Australian-born mothers from 1991 to 1994. Main outcome measures: Birthweight percentiles by gestational age. Results: During 1991-1994 Australian-born women gave birth to 769 077 live singleton infants. Of these, 28 230 (3.7%) were reported as births to Aboriginal or Torres Strait Islander women. Birthweight was missing for 581 (0.1%) births and gestational age was missing for 3014 (0.4%). An additional 3283 (0.4%) births were excluded because the recorded birthweights were extreme outliers for their recorded gestational ages. Indigenous women were more likely to be recorded as giving birth preterm (< 37 weeks' gestation) than non-indigenous women (11.6% v. 5.4%) and were more likely to give birth to small-for-gestational-age infants at term. After 34 weeks' gestation, the median birthweights of Indigenous infants were consistently lower than those of non-indigenous infants. At 40 weeks' gestation the difference in the median birthweights between these two groups was 160 g for males and 130 g for females. Conclusions: We present recent birthweight percentiles by gestational age based on national data in Australia. These percentiles provide current Australian norms for clinicians and researchers, and can provide a baseline for monitoring indigenous perinatal outcomes.