CIRCADIAN-RHYTHM OF FREQUENCY-DOMAIN MEASURES OF HEART-RATE-VARIABILITY IN PREGNANCY

Objective To examine frequency domain measures of heart rate variabili ty and their circadian rhythms in pregnancy. Design A longitudinal stu dy. Setting University hospital in Turku, Finland. Participants Sixtee n healthy women between 11 and 27 weeks of pregnancy; 12 women before pregnancy; and four women postpartum. Main outcome measures Heart rate variability as measured in frequency domain from 24-hour ambulatory e lectrocardiography. Results Pregnancy was associated with a lower stan dard deviation of R-R intervals (P < 0.01), with reduced very low (P < 0.05), low (P < 0.01), and high frequency (P < 0.05) power spectral c omponents of heart rate variability. The high frequency power was lowe r at night in pregnancy, but similar in the daytime in pregnant and no npregnant women. Conclusions Pregnancy is associated with an overall r eduction in heart rate variability, most markedly reflected in the low frequency component. This suggests altered baroreflex or sympathetic modulation of heart rate, and decreased vagal activation at night.