Approximate entropy: a regularity measure for fetal heart rate analysis

Area of Science:

• Perinatal medicine
• Biomedical signal processing
• Fetal physiology

Background:

• Fetal heart rate (FHR) monitoring is crucial for assessing fetal well-being during labor.
• Traditional FHR variability analysis may not capture all indicators of fetal compromise.
• Approximate entropy (ApEn) is a novel mathematical method for quantifying time-series regularity.

Purpose of the Study:

• To evaluate the utility of Approximate entropy (ApEn) in analyzing fetal heart rate (FHR) data.
• To determine if ApEn can differentiate between normal, presumed distressed, and acidotic fetuses.
• To investigate the correlation between FHR regularity, fetal acidosis, and labor events.

Main Methods:

• ApEn was calculated for hourly FHR data from three groups: normal labor, presumed fetal distress, and acidotic fetuses.
• FHR tracings were analyzed for regularity using ApEn values.
• Statistical comparisons were made between ApEn values and cord blood pH levels.

Main Results:

• Acidotic fetuses exhibited significantly lower ApEn values (more regularity) compared to normal and nonacidotic distressed fetuses (P < .00003).
• 28% of hourly ApEn values in acidotic fetuses were below 0.8, versus 5% in the combined normal and nonacidotic distressed groups.
• Hourly ApEn deviations often correlated with drug administration or physiological events like cord compression.

Conclusions:

• Extremely regular FHR patterns, as measured by ApEn, are associated with a higher probability of fetal acidosis.
• ApEn offers a valuable tool for detecting subtle FHR changes indicative of fetal compromise, potentially beyond traditional variability measures.
• ApEn analysis may enhance the detection of fetal distress and acidosis during labor.