Objective: Our purpose was to evaluate the influence of employment and physical exertion on pregnancy outcome as quantified by kilocalories expended each day.
Study design: This prospective study assessed 2743 pregnant women who received prenatal care and were delivered at the major perinatal center in Western Australia between May 1989 and November 1991. All women completed an extensive questionnaire on their social, medical, psychosocial, and economic circumstances. The women were allocated to five groups on the basis of kilocalorie expenditure per day.
Results: The characteristics of women in each energy expenditure group were different, with those in the least-expenditure group being younger and shorter, more likely to be living in worse socioeconomic conditions, smoke cigarettes, be nulliparous, and to be of an ethnic group other than white. After confounding effects were adjusted, women in the medium energy expenditure group were delivered of babies of higher birth weight than were women in other groups. However, the differences in birth weight between the energy expenditure categories were small, and mean birth weights within each group were within the normal range. Women in the medium energy expenditure group also had fewer incidences of prelabor rupture of membranes and women in the lower energy expenditure category had increased risks of antepartum admission to the hospital and preterm birth. A variety of other differences were observed in pregnancy outcomes for women in each of the categories of energy expenditure, but most of these differences were explained by the characteristics of the women in each expenditure level rather than the exercise pattern itself.
Conclusion: These results indicate that the effects of daily energy expenditure on pregnancy outcome are not great. Enthusiasm for counseling pregnant women of the benefits or hazards of extremes in daily activity should be tempered by the relative lack of an effect and the fact that most apparent differences are due to confounding variables rather than the exercise itself.