Effects of behavioral and medical variables on fetal growth retardation.

Cigarette smoking, indulging in certain drugs, restricting maternal weight gain in pregnancy, failing to obtain sufficient prenatal care, undertaking pregnancy at too early or too advanced on age, and being underweight for height at conception have in the past been identified with either increased premature births or births of term infants with fetal growth retardation. Each of these seven variables contains an element of maternal choice and has therefore been labeled by us as a behavioral variable. The combined group of mothers having these seven behavior variables was compared to a smaller group of mothers with medical complications and to a control group of mothers with neither behavioral nor medical variables. In the control group, there was a remarkably low incidence of premature births under 37 weeks (1 per cent), of term infants who had short body lengths at birth for their fetal ages (1.4 per cent), and of low-birth-weight infants (1 per cent). As the number of seven behavioral variables increased from none to three or more per pregnancy, the incidences of premature births, of short-for-dates term infants, and of low-birth-weight infants increased proportionately and significantly. The incidences of these seven behavioral variables, occurring either singly or in combination, were inverse to the mothers' socioeconomic status. However, the incidences of premature births, of growth-retarded term infants, and of low-birth-weight infants were high among mothers who had two or more behavioral variables in their pregnancies regardless of the mothers' socioeconomic status. The group of mothers with behavioral variables in comparison to the smaller group of mothers with medical complications had lower incidences but higher absolute numbers of premature infants, of growth-retarded term infants, and of low-birth-weight infants. Mothers who had medical complications as well as behavioral variables had more growth-retarded term infants than mothers with medical complications alone.