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.
PIP: Maternal cigarette smoking is associated with prematurity, small for gestational age babies, and increased perinatal morbidity and mortality. To study the possible mechanisms involved, 15 women 36-41 weeks pregnant were each given 1 cigarette with a nicotine content of 1.05 mg. Doppler ultrasonography was used to monitor the fetal heart rate, systolic and diastolic pressure in the uterine and umbilical arteries and umbilical and uterine blood velocities. The uterine systolic/diastolic ratio was not significantly elevated, but in the fetus the heart rate was significantly elevated and remained so throughout the study, and the mean umbilical systolic/diastolic ratio was significantly elevated and remained so for 30 minutes. This increased systolic/diastolic ratio in the umbilical artery is similar to that seen in fetuses with intrauterine growth retardation and is indicative of increased vascular resistance of the placenta from the fetal side, which may impair oxygen exchange across the placenta.