Antepartum fetal heart rate variability and intervillous placental blood flow in association with smoking.

Intervillous placental blood flow and indices of fetal heart rate variability were measured from seven healthy pregnant women in the last trimester of pregnancy, once before and twice after smoking one cigarette. A blood flow reduction was observed in seven, a rise in five, and no change in two measurements. When intervillous placental blood flow decreased both indices of variability decreased (p less than 0.001), and when it increased the short-term component of fetal heart rate variability increased more significantly (p less than 0.001) than did the long-term component (p less than 0.01).