Australian national birthweight percentiles by gestational age

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Abstract
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 769077 live singleton infants. Of these, 28230 (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 130g 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.