International variations in intrauterine growth.

International variations in intrauterine growth have consistently been judged in terms of average birthweight, low birthweight or birthweight-for-gestational age criteria. Neither of these provide an appropriate assessment of fetal growth. Notwithstanding these limitations the available evidence indicates that variations in growth, both within and among populations, relate predominantly to differences in the prevalence of factors that restrain growth rather than to inherent differences in growth potential. The evidence also indicates that differences in the frequency of low weight-for-gestation among populations do not only reflect factors that restrict fetal growth. They are also intimately linked to variations in gestational age and to frequencies of preterm birth in particular. Hence, if weight-for-gestational standards are to become more informative and more universally applied than they have been so far, it may be useful to acknowledge their limitations more explicitly and simplify their implementation in a wider range of communities.