[Reference birthweights for the Argentine population by multiplicity of birth, sex, and gestational age]

To develop new and improved reference birthweights for the Argentine population as a whole with a breakdown by gestational age (GA), sex and multiplicity of birth.

The population studied included all live births resulting from single (n = 3,478,286) and double (n = 57,654) births in Argentina during the period 2003- 2007. The probable errors in classifying GA on the basis of last menstruation were corrected using normal mixture models. The percentiles were obtained by quantile regression, which also made it possible to smooth out the curves.

Birthweight curves for single births were obtained between weeks 22 and 43 of gestation, and curves for double births between weeks 24 and 41, with a breakdown by the sex of the neonate. Compared with those of previous studies, these reference birthweights do not overestimate the proportion of live births large for their GA. An increase in birthweight was also observed during the period of study.

The proposed curves have the advantages of being based on large numbers, of being representative of the most recent Argentine births, of distinguishing the number of births and the sex of the neonates, and of minimizing GA classification errors. They are therefore a useful tool for measuring inequalities and thus identifying population groups at higher risk of adverse perinatal events.