Autonomic changes during pregnancy: assessment by spectral heart rate variability analysis.

The aim of this study was to investigate cardiovascular autonomic balance in normal pregnancy through spectral analysis of heart rate variability. For this purpose, electrocardiograms were recorded in 8 nonpregnant women and in 32 pregnant women at 10-39 weeks of gestation. Low-/high-frequency peak (LF/HF) ratio was used as an indirect index of sympathovagal balance. In left lateral recumbency, the LF/HF ratio was lower in pregnant women than in control subjects at all gestational ages. The LF/HF ratio was not affected by turning from left lateral to supine recumbency in control subjects, whereas it significantly increased in pregnant women (eg, from a mean +/- SD of 1.05 +/- 0.81 to 2.18 +/- 1.69 after the 33rd week of gestation). Handgrip at low intensity remarkably increased the LF/HF ratio both in control subjects (from 2.21 +/- 2.76 to 2.73 +/- 1.91) and in pregnant women (from 1.28 +/- 1.17 to 2.24 +/- 0.95 at 34-39 weeks of gestation). The results suggest that a rearrangement of autonomic tone takes place in normal pregnancy, which could be interpreted either as a shift of autonomic balance toward a relative vagal predominance or as the consequence of attenuation of baroreflexes.