Circulatory changes in the fetal aorta after maternal smoking.

The acute cardiovascular responses of the human fetus to maternal smoking of one cigarette were studied in 10 healthy pregnant women. Following maternal smoking, a significant increase was found in the nicotine concentration in maternal plasma accompanied by a significant increase in the fetal heart rate. The flow velocity was recorded in the fetal descending aorta by combining real-time ultrasonography and the 2 MHz pulsed Doppler technique and the waveform of the maximum blood velocity was analysed. The duration of the acceleration part of the pulse cycle (start-to-peak time) remained unchanged during the study period. The least diastolic blood velocity increased significantly after smoking. The pulsatility index fell significantly during the first 5 min after smoking, probably as the consequence of fetal tachycardia, but was normal again at 10 min. The rising slope rose significantly within the first 10 to 20 min after the onset of smoking. The results indicate, that, following maternal smoking of one cigarette, fetal central circulation increases but peripheral resistance is unchanged.