Acute effect of cigarette smoking on the fetal heart nonstress test.

A major limitation in the use of the nonstress test (NST) has been the high frequency of nonreactive NSTs in the absence of fetal distress. Exogenous factors causing loss of fetal heart rate reactivity (FHRR) have not been fully evaluated, although it has previously been shown that chronic smokers have an increased incidence of nonreactive NSTs in the absence of fetal distress. A group of chronically smoking high-risk pregnant women at 31 to 44 weeks' gestation was studied to determine if the acute effects of smoking caused the NST to become nonreactive. After a reactive NST was obtained, each patient smoked 1 cigarette and the effects of the fetus were observed. Twenty-six studies were performed on 25 patients. A transient mild elevation of baseline fetal heart rate was noted after smoking in several studies; however, no significant change was found in FHRR, indicating that the acute effects of smoking a single cigarette are not responsible for the increased incidence of nonreactive NSTs in smokers.