• J O E H van Laar, C H L Peters, R Vullings, S Houterman, and S G Oei.
• Department of Obstetrics and Gynecology, Máxima Medical Centre, De Run 4600, 5504 DB, Veldhoven, The Netherlands. joehvanlaar@hotmail.com
• Early Hum. Dev. 2009 Dec 1; 85 (12): 795-8.

BackgroundSpectral analysis of fetal heart rate variability is promising for assessing fetal condition. Before using spectral analysis for fetal monitoring it has to be determined whether there should be a correction for gestational age or behavioural state.AimsCompare spectral values of heart rate variability between near term and post term fetuses during active and quiet sleep.Study DesignCase-control. Cases had a gestational age of > or =42 weeks; controls were 36 to 37 weeks. Fetuses were matched for birth weight percentile.SubjectsSTAN registrations from healthy fetuses. For each fetus one 5-minute segment was selected during active and one during quiet sleep.Outcome MeasuresAbsolute and normalized low (0.04-0.15 Hz) and high frequency power (0.4-1.5 Hz) of heart rate variability.ResultsTwenty fetuses were included. No significant differences were found between cases and controls in absolute (481 and 429 respectively, P=0.88) or normalized low (0.78 and 0.80 respectively, P=0.50) or absolute (41 and 21 respectively, P=0.23) or normalized high frequency power (0.08 and 0.07 respectively, P=0.20) during active state. During rest, normalized low frequency power was lower (0.58 and 0.69 respectively, P=0.03) and absolute (16 and 10 respectively, P=0.04) and normalized high frequency power were higher (0.21 and 0.14 respectively, P=0.01) in cases compared to controls. Absolute and normalized low frequency power were higher during active state compared to rest in both groups (all P values <0.05).ConclusionsWe found sympathetic predominance during active state in fetuses around term. Post term parasympathetic modulation during rest was increased compared to near term.

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