- The relationship between physical activity at home and at work during pregnancy and preterm birth was studied. Using a case-control design, 99 women who delivered preterm were compared with 189 women who had term deliveries. The risk of preterm birth was tested in relation to characteristics of work in and outside the home. All women were interviewed post-partum before discharge. There were no statistically significant differences between the groups in relation to sociodemographic and obstetrical factors, but level of education was significantly lower in the study group versus the control group (p = 0.001). Women who delivered preterm had devoted less time 3 months prior to delivery to household chores (mean of 3.7 hours vs. 4.8 hours in the control group, p = 0.002). They also had spent less time walking around the home than the controls (1.2 vs. 1.5 hours, p = 0.02). There were no differences between the groups in relation to physical activity outside the home, not during working hours, nor in duration of work. Significantly fewer women who delivered preterm were active in sports (odds ratio 0.22; 95% confidence interval 0.50-0.65; p = 0.002). A low level of education was significantly related to the risk of preterm birth, which may have resulted from lesser compliance with their physician's recommendations. It appears that in women not used to significant physical activity but who had access to adequate prenatal care, physical effort during pregnancy was not related to a higher risk of preterm birth.