Many factors contribute independently or jointly to the cause and pathogenesis of low birth weight. Attempts to identify these factors in a given population, however, are usually unsuccessful, and conclusions are equivocal. Among the variables related to fetal growth, socioeconomic status and size of the mother consistently show positive correlations. Thus, incidence of low birth weight, defined as less than 2,501 gm (5.5 lb),1 is lowest in the nations with the highest standard of living.2 Although the United States is among the most developed nations, its incidence of low birth weight is higher than that of some European countries,3 primarily because of the high incidence of low birth weight among its population groups of low socioeconomic class.
The problem is more serious in developing nations, but it is extremely difficult to assess there because of inadequacy or lack of statistical data. Data on birth weight in these
Mata LJ, Urrutia JJ, Kronmal RA, Joplin C. Survival and Physical Growth in Infancy and Early Childhood: Study of Birth Weight and Gestational Age in a Guatemalan Indian Village. Am J Dis Child. 1975;129(5):561–566. doi:10.1001/archpedi.1975.02120420017006
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