Marked fetal acidosis and specific changes in power spectrum analysis of fetal heart rate variability recorded during the last hour of labour

Abstract

Objective To assess whether intrapartum acidosis affects specific components of fetal heart rate variability.Design Prospective clinical study.Setting Twelve Nordic delivery units.Subjects 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 ¼ 15) and the control group (cord arterial pH !7.05 at birth, n ¼ 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. Main outcome measures 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 ¼ 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 ¼ 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.

Multifractal Analysis of Fetal Heart Rate Variability in Fetuses with and without Severe Acidosis during Labor

“…[30][31][32] Studies from Siira et al and Salamalekis et al showed a predominant increase in the low-frequency domain and, therefore, a higher low-to high-frequency ratio in acidotic fetuses, consistent with the increase in sympathetic system activity induced by hypoxia. 16,19,31,32 Interestingly, one of the multifractal parameter we studied (zeta(2)), which is related to low-to highfrequency ratio, also showed a predominant increase in sympathetic component when fetal acidosis developed. [31][32][33] One of the strengths of multifractal analysis is also to provide multiple parameters to explore signal variability, particularly for complex signals that can definitely not be appropriately described using only one parameter.…”

“…Multifractal analysis has the strength to reach results consistent with previous studies about variability using other mathematical methods, such as the classical spectral analysis, and to provide additional information that could help in discriminating fetuses with acidosis from nonacidotic fetuses. 2,7,16,18 Consistent with previous studies and physiopathologic mechanisms, the results of this study showed that variability is lower in the acidotic fetuses when compared with the nonacidotic fetuses as demonstrated by higher values of C 1 , h min , h Max , and zeta(2) in group C. 2,7,16,18 Moreover, multifractal analysis focuses on characterizing the evolution of signal variability in a collection of windows of growing size, identified by the method itself according to the intrinsic data characteristics and not chosen a priori. Our results showed that windows of interest for multifractal analysis ranged from 4 to 64 seconds.…”

“…11 Second, these windows from 4 to 64 seconds correspond to a frequency scale varying from 0.015 Hz to 1 Hz, which cover the frequency domains of adult heart rate. 8,16 In spectral analysis, the low-frequency domain (from 0.04 to 0.15 Hz) mainly corresponds to the sympathetic activity. The high-frequency band (from 0.15 to 1 Hz) corresponds mainly to the parasympathetic activity.…”

“…The high-frequency band (from 0.15 to 1 Hz) corresponds mainly to the parasympathetic activity. 8,16 The low-to high-frequency ratio therefore reflects the balance between the sympathetic and the parasympathetic activities. [30][31][32] Studies from Siira et al and Salamalekis et al showed a predominant increase in the low-frequency domain and, therefore, a higher low-to high-frequency ratio in acidotic fetuses, consistent with the increase in sympathetic system activity induced by hypoxia.…”

“…[8][9][10][11][12][13][14][15] Few 1 studies, based on these statistical tools, focused on FHR variability analysis during labor to detect hypoxia or acidosis, with variable results. [16][17][18][19][20][21] Multifractal analysis is a recent technique that aims at providing detailed and elaborated analysis of data variability, particularly adapted for characterization of nonstationary and complex signals like FHR. 22,23 Although variability is clinically analyzed by considering the largest difference in data (referred to as ''oscillation'') observed within a sliding time window of a priori chosen size (usually 1 minute), multifractal analysis focuses on characterizing the evolution of the variability measured in a collection of windows of different growing sizes, within a relevant range that is a posteriori and adaptively determined by the method itself.…”