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Complementary and non-coincident increases in heart rate variability and irregularity during fetal development
L A Fleisher1, J A Dipietro, T R Johnson
1Johns Hopkins Medical Institutions, Baltimore, Maryland, USA.
Clinical Science (London, England : 1979)
|April 1, 1997
Summary
Fetal heart rate variability and irregularity increase with gestational age. These changes occur independently in males, suggesting distinct gender-based developmental pathways in utero.
Area of Science:
- Perinatology and Fetal Development
- Cardiovascular Physiology
- Biostatistics
Background:
- Heart rate variability (HRV) is assessed using standard deviation (SD) and approximate entropy (ApEn) to measure regularity and irregularity, respectively.
- Understanding the evolution of fetal heart rate (FHR) variability and irregularity during gestation is crucial for assessing fetal well-being.
- The relationship between SD and ApEn and their independent changes during fetal development requires further investigation.
Purpose of the Study:
- To investigate the developmental trajectories of FHR standard deviation (SD) and approximate entropy (ApEn) from 20 to 36 weeks gestation.
- To determine if the evolution of FHR irregularity is coincident with or distinct from the evolution of FHR variability.
- To explore potential sex-based differences in the development of FHR variability and irregularity.
Main Methods:
- Fetal heart rate (FHR) was recorded for 15 minutes at 4-week intervals (20-36 weeks gestation) in 14 males and 17 females using a fetal actocardiograph.
- Standard deviation (SD) was calculated to assess heart rate variability.
- Approximate entropy (ApEn), including normalized ApEn, was used to quantify heart rate irregularity.
Main Results:
- Mean heart rate decreased significantly with gestational age (P < 0.05).
- FHR standard deviation (SD) significantly increased from 20 to 36 weeks gestation (P < 0.05) and was similar between sexes (P = 0.57).
- Fixed and normalized approximate entropy (ApEn) significantly increased with gestational age (P < 0.01), indicating increasing irregularity. Normalized ApEn increased in males but remained constant in females, suggesting sex-specific patterns of irregularity development. ApEn was lower in males at 20 weeks but similar by 28 weeks.
Conclusions:
- Fetal heart rate variability and irregularity increase independently in male fetuses but not in female fetuses during development.
- These findings suggest an increase in the coupling of emerging neural networks with gestational age, with distinct sex-based developmental patterns.
- Analyzing both SD and ApEn provides complementary information on FHR regulation, highlighting sex differences in fetal development consistent with other physiological systems.