Similarities between maternal and fetal RR interval tachograms and their association with fetal development

Abstract

An association between maternal and fetal heart rate (HR) has been reported but, so far, little is known about its physiological implication and importance relative to fetal development. Associations between both HRs were investigated previously by performing beat-by-beat coupling analysis and correlation analysis between average maternal and fetal HRs. However, studies reporting on the presence of similarities between maternal and fetal HRs or RR intervals (RRIs) over the short term (e.g., 5-min) at different gestational ages (GAs) are scarce. Here, we demonstrate the presence of similarities in the variations exhibited by maternal and fetal RRl tachograms (RRITs). To quantify the same similarities, a cross-correlation (CC) analysis between resampled maternal and fetal RRITs was conducted; RRITs were obtained from non-invasive electrocardiogram (ECG). The degree of similarity between maternal and fetal RRITs (bmfRRITs) was quantified by calculating four CC coefficients. CC analysis was performed for a total of 330 segments (two 5-min segments from 158 subjects and one 5-min from 14 subjects). To investigate the association of the similarity bmfRRITs with fetal development, the linear correlation between the calculated CC coefficients and GA was calculated. The results from the latter analysis showed that similarities bmfRRITs are common occurrences, they can be negative or positive, and they increase with GA suggesting the presence of a regulation that is associated with proper fetal development. To get an insight into the physiological mechanisms involved in the similarity bmfRRITs, the association of the same similarity with maternal and fetal HR variability (HRV) was investigated by comparing the means of two groups in which one of them had higher CC values compared to the other. The two groups were created by using the data from the 158 subjects where fetal RRI (fRRI) calculation from two 5-min ECG segments was feasible. The results of the comparison showed that the maternal very low frequency (VLF) HRV parameter is potentially associated with the similarity bmfRRITs implying that maternal hormones could be linked to the regulations involved in the similarity bmfRRITs. Our findings in this study reinforce the role of the maternal intrauterine environment on fetal development.

Keywords: fetal developement; fetal programming; heart rate vaiability; maternal-fetal RRI similarity; very low frequency.

FIGURE 1

Example of normalized and resampled maternal and fetal RR interval tachograms (RRITs). (A) The figure shows an example of maternal (blue) and fetal (orange) RRITs before resampling, the amplitudes are normalized in this figure by using Eq. 1. (B) The figure shows resampled RRITs, resampling was done by taking the average of RRI per 2 s.

FIGURE 2

Summary of data analysis. The flowchart provides a graphical summary of the steps that were followed to analyze the data. In Step 1, 5-min extraction of fetal electrocardiogram (fECG) was successful in 172 out of 195 subjects. In step 2, additional extraction of 5-min segments was successful in 158 out of the 172 subjects. Both in step 1 and step 2 cross-correlation (CC) and maternal and fetal heart rate variability (HRV) analyses were performed for the extracted 5-min segments. In step 3, a comparison of means analysis was performed to compare between group 1 and group 2 in terms of maternal and fetal HRV analysis. Group 2 has higher CC1 or CC3 values compared to group 1.

FIGURE 3

Demonstration of positive and negative similarity trends between maternal and fetal RR interval tachograms (bmfRRITs). Figures (A–C) show examples of positive similarity trends in which maternal (blue) and fetal (orange) RRITs change in the same direction. Figures D, E and F (D–F) show examples of negative similarity trends in which maternal and fetal RRITs change in opposing directions. The upper panels in Figures (D–F) show the original signals while the lower panels show the original fetal signal with the maternal signal inversed. (A) The record belongs to a mother who had no records of medical complications, gestational age (GA): 20 weeks. (B) The record belongs to a mother with a record of uterine/appendix disease, GA: 23 weeks. (C) The record belongs to a mother with a medical record of respiratory disease and uterine/appendix disease, GA: 20 weeks. (D) The record belongs to a mother with a medical record of autoimmune disease, gestational age (GA): 39 weeks. (E) The record belongs to a mother who had a blood disease, GA: 33 weeks. (F) The record belongs to a mother with no records of medical complications, GA: 2 weeks.

FIGURE 4

Scatter plots for visualizing the correlations described in Table 1. (A) Cross-correlation (CC) coefficients – gestational age (GA). (B) Fetal features—GA. (C) Maternal features – GA. Thick black lines indicate the best-fitting line. The dotted black lines indicate the 95% confidence interval (CI). The sample size is 172. r indicates Spearman correlation coefficients.