A method for dyadic cardiac rhythmicity analysis: Preliminary evidence on bilateral interactions in fetal–maternal cardiac dynamics

Cardiac activity responds dynamically to metabolic demands and neural regulation. However, little is known about this process during pregnancy. Reports show occasional fetal-maternal heart rate couplings, but it has remained unclear whether these couplings extend to more complex oscillatory patterns of the heart rhythm. We developed a framework of time-varying measures of heart rate and rhythm, to test the presence of co-varying patterns in concurrent maternal and fetal measures (late pregnancy dataset, n = 10, and labour dataset, n = 12). These measures were derived from first and second-order Poincaré plots, with the aim to describe changes in short- and long-term rhythmicity, but also the dynamic shifts in acceleration and deceleration of heart rate. We found episodes of maternal-fetal co-varying patterns of cardiac rhythm in all the measures explored, in both datasets (at least 90% of the dataset presented a significant maternal-fetal correlation in each measure, with P < 0.001), with dynamic delays suggesting bilateral interactions at different time scales. We also found that these couplings intensify during labour (test between late pregnancy vs. labour datasets, P < 0.0015 in all second-order Poincaré plot-derived measures). While most literature suggests that the fetal heart responds to maternal breathing patterns or contractions, we propose the possibility that the fetal heart may also have a signalling function in the context of co-regulatory mechanisms and maternal inter-organ interactions. Understanding these complex visceral oscillations in utero may enhance the assessment of a healthy fetal development.