Quantitative assessment of the relationship of slow-wave heart rate oscillations and motor activity in rat fetuses with maternal respiratory and cardiac activity

A correlation between slow-wave processes in the female–fetus system was experimentally studied and mathematically analyzed in rat fetuses retaining placental connection with the maternal organism during the final 4 days of gestation. Simultaneous recording of the physiological state’s parameters of females and fetuses revealed a relationship between the respiration and heart rate oscillations in the near-minute and multi-minute ranges. The relationship between maternal and fetal heart rates was strongest on the 17th and 20th days of gestation and somewhat weaker on the 18th–19th days. The mechanism underlying female–fetus synchronization of heart rate oscillations is unclear. There are two hypothetical possibilities: either the oscillation driver sharing similar parameters in mother and fetus, or the maternal rhythm exerting a direct influence on the fetus.