Midtrimester fetal heart rate variability and maternal hemodynamics in association with smoking

Maternal heart rate (MHR), blood pressure (BP), the differential index (DI) describing the short-term component of fetal heart rate (FHR) variability, and the interval index (II) describing the long-term component were measured in eight subjects in the midtrimester before, during, and after the mothers smoked a standard cigarette. The analyses of FHR variability were performed by an "on-line" method with an abdominal fetal electrocardiogram used as a triggering signal and with a sample time of 1 minute. An increase of MHR, FHR, and BP with a concomitant decrease of II was observed. Unlike our findings regarding the third trimester, no significant change of DI was observed. A correlation analysis revealed fetomaternal hemodynamic relationships different from those in the third trimester: There was a negative correlation between DI and FHR (p less than 0.01) and between DI and MHR (p less than 0.01). There was a positive correlation between FHR and MHR (p less than 0.001). Unlike our findings regarding the third trimester, no correlation was found between DI and BP or between II and MHR. We suggest that the midtrimester fetus shows the narcotic effect (decrease of II) of one cigarette, as does the term fetus, but fails to show the hypoxic effect (decrease of DI), which has been observed in the term fetus.