The epidemiology of low birthweight.

In this paper, I review the epidemiology of low birthweight (LBW). I begin by defining LBW and emphasizing the distinction between infants who are born early (preterm) and those who are born small for their gestational age (SGA). I then review data on the global burden of preterm birth and SGA and the evidence bearing on whether 'one size fits all', i.e. whether a single birthweight (or birthweight for gestational age) cutoff is appropriate for different regions and population subgroups. I summarize what is known about the etiologic determinants of preterm and SGA birth, how they differ among countries of varying socioeconomic development and prevalence of risk factors, and how they are changing over time. I conclude with a critical appraisal of LBW prevention as a public health priority and argue that reducing fetal and infant mortality is a more important and achievable target for intervention.