Prenatal Behavioral Contagion: Maternal Yawning Triggers Fetal Resonance

The prenatal period is a critical window for the emergence of sensorimotor coordination and early relational processes. Within this framework, yawning—a stereotyped behavior linked to arousal regulation and social contagion—offers a unique opportunity to explore maternal-fetal relationships before birth. While contagious yawning has been extensively studied in postnatal contexts, its presence and developmental role in utero remain unexplored. This study investigated whether fetal yawning behavior is modulated by maternal yawning, suggesting a primitive form of behavioral contagion within the dyad. Thirty-six pregnant participants were exposed to video stimuli designed to elicit yawns, while fetal facial movements were recorded using 2D ultrasound. Maternal and fetal yawning frequencies were analyzed across four conditions: baseline, maternal still-face, maternal mouth opening/closing movements, and maternal yawning. Fetal and maternal time series were further examined using Cross Recurrence Quantification Analysis (CRQA), and an LSTM-based neural network was employed for automated behavioral classification. Results showed a significant increase in fetal yawns following maternal yawning, but not during control conditions, indicating selective behavioral responsiveness. CRQA revealed enhanced temporal structure in true mother-fetus dyads compared to shuffled pairs, suggesting non-random coordination. The LSTM model accurately distinguished yawning from other facial actions, supporting the reliability of the behavioral data. These findings provide the first evidence of prenatal yawning contagion and support the notion that behavioral alignment may reflect embodied mechanisms of attunement that precede postnatal social engagement, offering new insights into the developmental origins of intersubjectivity.