Key result
Active labor at term was associated with decreased short-term fetal heart rate variability (PRR5 28.84% vs 37.13%, p=0.03) compared to the third trimester, indicating decreased vagal modulations.
Why the study?
Fetal heart rate variability is essential to monitor fetal well-being, but applying symbolic dynamics to compare fetal heart rate variability between the third trimester and active labor required evaluation.
Does fetal heart rate variability differ between the third trimester of pregnancy and active labor at term in low-risk pregnancies?
Observational (n=21)
No
Does fetal heart rate variability differ between the third trimester of pregnancy and active labor at term in low-risk pregnancies?
Fetal heart rate variability analysis using symbolic dynamics shows decreased vagal modulation and higher adrenergic response during active labor compared to the third trimester.
Decreased short-term fHRV during labor signals autonomic shifts; leaves open whether symbolic dynamics adds clinical value beyond standard monitoring.
Fetal heart rate variability (fHRV) is an essential source of information to monitor fetal well-being during pregnancy. This study aimed to apply a nonlinear approach, known as symbolic dynamics (SD), for comparing human fHRV in the third trimester of pregnancy during active fetal state (TT) and active labor at term (P). We performed a longitudinal, prospective, descriptive, and comparative study composed of 42 longitudinal recordings of 5-minutes of fetal heartbeat interval series. Recordings were collected from 21 low-risk, healthy, pregnant women attending the Maternal and Child Research Center (CIMIGen), Mexico City. We calculated relevant linear parameters of fHRV between TT and P stages, such as the percentage of differences between adjacent RR intervals >5 ms (PRR5, related to vagal modulations) and other SD parameters such as the percentage of no variations between three successive symbols (%0V, reflects sympathetic modulations) and the probability of low variability with a threshold of 4 ms (POLVAR4, associated with a low variability). We identified statistical differences for PRR5 between TT and P (37.13% [28.47-47.60%] vs. 28.84% [19.36-36.76%], p = 0.03), respectively. Also, for 0V% (65.66% [59.01-71.80%] vs. 71.14% [65.94-75.87%], p = 0.03) and for POLVAR4 values (0.06 [0.04-0.11] vs. 0.15 [0.09-0.24], p = 0.002), respectively. Our results indicate that during parturition, the short-term fetal fHRV is decreased, showing a decreased vagal modulations and higher adrenergic response of the heart. These autonomic modifications may result from the fetal response to the stressful inflammatory challenge of labor. We thus confirmed that the analysis of the SD applied to fHRV time series could be a potential clinical biomarker to differentiate the fetal autonomic cardiac condition at different stages of pregnancy.
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Montalvo-Jaramillo et al. (2020) conducted an observational in Pregnancy (n=21). Active labor at term vs. Third trimester of pregnancy was evaluated on Percentage of differences between adjacent RR intervals >5 ms (PRR5) (p=0.03). Active labor at term was associated with decreased short-term fetal heart rate variability (PRR5 28.84% vs 37.13%, p=0.03) compared to the third trimester, indicating decreased vagal modulations.
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