A customized birthweight centile calculator developed for an Australian population.

Customized percentiles improve the differentiation between constitutional and pathological smallness of the fetus and the neonate. We studied data from 12420 pregnancies in Sydney to develop Australian coefficients for customized fetal growth and birthweight centiles. Significant coefficients were derived for maternal height, weight, parity and ethnic origin as well as gestational age and the baby's gender. Standardised comparison with results from previous reports from England and New Zealand shows marked similarities in the predicted birthweight at term, confirming international applicability of the concept of adjusting for constitutional factors when calculating the growth potential of an individual fetus.