AbstractThe effects of a standardized exercise test on intervillous placental blood flow were studied in 13 hypertensive, 10 diabetic and 8 cholestatic pregnant women in late pregnancy, and the results were compared with those of a normal control group. Analysis of variance for repeated measures revealed that in all the pathologic groups, placental blood flow was lower than in the controls. In all groups placental blood flow rose slightly 1 min after the cessation of exercise. The diabetics showed a decreased placental blood flow 30 min after the cessation of the exercise test (p>0.021. In diabetics, a fall was found in stroke volume, from 63 ± 12 ml (mean ± SD) before the exercise to 53 ± 11 ml 30 min after the cessation of exercise (p>0.051, and a rise in peripheral vascular resistance, from 1540± 200 (mean± SD) dynes/cm5before exercise to 1750 ± 390 dynes/cm530 min after the cessation of exercise (p>0.051. Pre‐eclamptic patients had a higher peripheral vascular resistance than had normal controls. Pre‐eclamptic, diabetic and cholestatic patients had lower cardiac index values than the normal subjects. The difference was significant in the pre‐eclamptic and diabetic patients at 30 min after the cessation of exercise. Maternal heart rate, and systolic, diastolic and mean arterial blood pressures rose significantly from values at rest to values at the end of exercise in all groups. One of the pre‐eclamptic patients showed a 74% decline in placental blood flow 1 min after the cessation of exercise coincident with fetal bradycardia. 30 min after the cessation of exercise the flow was 51% of the pre‐exercise value with reactive fetal heart rate tracing. It is concluded that at least in pregnancies complicated by hypertension or diabetes a submaximal short exercise can cause a fall of cardiac index and placental blood flow and, therefore should be avoided in