Effects of maternal smoking on circulating catecholamine levels and fetal heart rates.
Eight pregnant chronic cigarette smokers were studied after 34 weeks of gestation to determine the effects of acute cigarette (two nonfilter cigarettes) inhalation on maternal neuroendocrine and cardiovascular changes and on the fetus. Cigarette smoking was found to induce rapid (within 2 1/2 minutes) elevations in maternal plasma norepinephrine and epinephrine levels and this was associated with a rise in maternal pulse and blood pressure. These changes are followed, with a 5 minute lag time, by a significant increase in fetal heart rate. A relatively slow but sustained increase in maternal carboxyhemoglobin (HbCO) concentration occurred. The time course of this increase in HbCO did not seem to be responsible for the acute changes in fetal heart rate. Maternal cortisol levels also showed a slow but sustained elevation. Our present findings, together with data obtained from animal models, suggest that cigarette smoking during pregnancy induces fetal hypoxia through two independent but additive pathways: (1) An acute effect is caused by nicotine activation of adrenergic discharge, resulting in vasoconstriction, a decreased uterine perfusion, and a consequent transient fetal tachycardia, and (2) a delayed but prolonged increase in HbCO may cause a sustained reduction of fetal oxygenation.