Joint symbolic dynamics identifies differences in the maternal-fetal cardiac coupling between nonlaboring and laboring women

•JSD was applied for evaluating maternal and fetal heart rate interactions in labor.•A significant increment of the short-term MFCC was found in laboring women.•MFCC is probably influenced by the uterine contractile activity during labor.•JSD is a promising tool for measuring MFCC in labor and nonlabor states. There is a growing interest in investigating maternal-fetal cardiac coupling (MFCC) to identify the physiological processes involved in fetal development and well-being during pregnancy. No evidence of MFCC has been reported during active labor, a critical stage at the end of pregnancy for the mother-child binomial. Therefore, this exploratory study compares the short-term MFCC between nonlaboring and laboring women by applying nonlinear joint symbolic dynamics (JSD). Forty-four pairs of maternal-fetal RR interbeat intervals series were longitudinally analyzed during the third trimester of pregnancy (TT, 36.5 ±1.7 weeks of gestation) and later at active parturition at term (P, 39.4 ±1.2 weeks gestation), corresponding to low-risk pregnant women (N=22). For each pair of maternal-fetal interbeat intervals series at TT and P, a word distribution density matrix was calculated to assess general and partial coupling behavior. The JSD approach revealed changes in the MFCC, permitting the identification of differences between the TT and P conditions (p