Socioeconomic factors in relation to fetal growth in white infants.

Over 1,200 white mothers who were delivered consecutively at this medical center were classified in four different socioeconomic classes according to family affluence and occupations of the heat of the household. The frequency of low-birth-weight infants was highest in the lowest socioeconomic class. The high incidence of LBW infants in the lowest socioeconiomic group was not affected by any significant increase in number of mothers with medical problems or medical complications of pregnancy; it was dependent on the large number of mothers who were involved in four specific practices, largely of their own choosing, including low-weight gains, cigarette smoking, use of certain drugs during pregnancy, and refraining from all prenatal care. Mothers in the four socioeconomic classes who were not involved with these four specific practices (smoking, etc.) and whose pregnancies were free of medical problems and complications had uniformly low incidences of LBW infants and the mean birth weights of their infants were uniformly high and not significantly different. Unfavorable outcome of pregnancy with respect to fetal growth in this study appeared to depend less directly on socioeconomic circumstances than on the four specific maternal practices listed above.