Marked fetal acidosis and specific changes in power spectrum analysis of fetal heart rate variability recorded during the last hour of labour.
OBJECTIVE
To assess whether intrapartum acidosis affects specific components of fetal heart rate variability.


METHODS
Prospective clinical study.


METHODS
Twelve Nordic delivery units.


METHODS
Fetal heart rate variability was studied in 334 fetuses divided into two groups according to cord pH value: the acidotic group (cord arterial pH < 7.05 at birth, n= 15) and the control group (cord arterial pH > or =7.05 at birth, n= 319).


METHODS
In spectral analysis of fetal heart rate variability, frequencies were integrated over the total frequency band (0.04-1.0 Hz), low-frequency band (0.04-0.15 Hz) and high-frequency band (0.15-1.0 Hz). We also calculated the low-to-high frequency ratio.


METHODS
The spectral bands of fetal heart rate variability were compared between the acidotic and control fetuses.


RESULTS
We found that during the last hour of monitoring, baseline fetal heart rate gradually decreased, whereas total, low-frequency and high-frequency fetal heart rate variability initially increased but then, near the delivery, decreased in the acidotic fetuses when compared with the controls. Low-to-high frequency ratio was greater in the acidotic group during the whole study period (P= 0.002). Cord artery pH was inversely associated with total fetal heart rate variability (P < 0.001), low-frequency fetal heart rate variability (P < 0.001) and low-to-high frequency ratio (P= 0.004).


CONCLUSIONS
Marked fetal acidosis was associated with frequency-specific changes in fetal heart rate variability as reflecting the compensation ability of autonomic nervous activation during the last hour of labour.
Siira
Saila M
SM
Research Centre of Applied and Preventive Cardiovascular Medicine (CAPC), University of Turku, Kiinamyllynkatu 10, 20520 Turku, Finland.
Ojala
Tiina H
TH
Vahlberg
Tero J
TJ
Jalonen
Jarmo O
JO
Välimäki
Ilkka A
IA
Rosén
Karl G
KG
Ekholm
Eeva M
EM
D000138:Acidosis / Q000175:diagnosis* / Q000503:physiopathology; D015148:Cardiotocography / Q000592:standards; D036861:Delivery, Obstetric / Q000379:methods; D004562:Electrocardiography / Q000592:standards; D005260:Female; D005315:Fetal Diseases / Q000175:diagnosis* / Q000503:physiopathology; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D011247:Pregnancy; D011446:Prospective Studies; D013057:Spectrum Analysis / Q000592:standards; D013997:Time Factors; D014469:Umbilical Arteries