Effects of maternal cigarette smoking on fetal breathing and fetal movements.

The effect of cigarette smoking on fetal breathing and fetal movements was studied in 10 women with low-risk pregnancy of 34 to 38 weeks' gestation. A continuous Doppler ultrasound method was used to measure fetal breath intervals. Smoking two cigarettes caused a small increase in the rate of fetal breathing (p < 0.01), which persisted for 60 minutes; the proportion of time the fetus spent breathing was not changed. There was a decrease in the number of fetal movements felt by the mother. These findings are discussed in relation to the alleged pathophysiologic effects of tobacco smoking on the fetus.