Smoking in pregnancy affects the fetal heart: possible links to future cardiovascular disease

To investigate effects of maternal smoking on the fetal heart rate (FHR) in ambulatory patients using a portable fetal electrocardiogram recording device.

A prospective cohort study of 43 pregnant smokers and 43 non-smoking gestation-matched controls with uncomplicated singleton pregnancies. Smokers were divided into light (1-10) and moderate (11-20 cigarettes/d). The FHR was recorded for 16 h with smokers smoking at will, using an event button to record when they lit a cigarette. Fifty recordings were made in the patients' homes with 36 in ambulatory inpatients. Three consecutive 30-min epochs (before, during and after smoking) were compared with the controls.

Basal FHR was significantly lower before smoking in the foetuses of smokers compared with non-smokers (p = 0.048). During smoking, there was a significant dose-dependent fall in short-, long-term and true beat-to-beat variabilities (p = 0.004, p < 0.0001 and p = 0.024, respectively).

Maternal smoking leads to reversible changes in FHR variability that mimic those associated with an increased incidence of adverse cardiovascular events in adults. As heart rate and variability reflect the autonomic control of the heart, our findings suggest that maternal smoking interferes with the autonomic control of the FHR.