Maternal cigarette smoking: the effects on umbilical and uterine blood flow velocity.

Maternal and fetal effects of smoking one cigarette were assessed in 15 healthy women at 36 to 41 weeks' gestation with no obstetric complications. It was found that smoking was associated with increases in maternal heart rate and blood pressure, but there was no significant change in the uterine artery vascular resistance as measured by means of the systolic/diastolic velocity ratio. There also was an increase in the fetal heart rate as well as a highly significant rise in the systolic/diastolic velocity ratio of the umbilical artery. The responses suggest that smoking causes a direct increase in the vascular resistance of the placenta from the fetal side. This resistance may impair oxygen exchange across the placenta and contribute to the increased perinatal morbidity associated with smoking.