Fetal Sleep: A Cross-Species Review of Physiology, Measurement, and Classification
It addresses the underexplored problem of fetal sleep monitoring for clinicians and researchers, offering a comprehensive but incremental synthesis of existing knowledge.
This review synthesizes over eight decades of research on fetal sleep physiology, measurement, and classification, comparing patterns in humans and animal models to provide a foundation for developing non-invasive monitoring technologies for early diagnosis in prenatal care.
Fetal sleep is a relatively underexplored yet vital aspect of prenatal neurodevelopment. Understanding fetal sleep patterns could provide insights into early brain maturation and help clinicians detect signs of neurological compromise that arise due to fetal hypoxia or fetal growth restriction. This review synthesizes over eight decades of research on the physiological characteristics, ontogeny, and regulation of fetal sleep. We compare sleep-state patterns in humans and large animal models, highlighting species-specific differences and the presence of sleep-state analogs. We review both invasive techniques in animals and non-invasive modalities in humans. Computational methods for sleep-state classification are also examined, including rule-based approaches (with and without clustering-based preprocessing) and state-of-the-art deep learning techniques. Finally, we discuss how intrauterine conditions such as hypoxia and fetal growth restriction can disrupt fetal sleep. This review provides a comprehensive foundation for the development of objective, multimodal, and non-invasive fetal sleep monitoring technologies to support early diagnosis and intervention in prenatal care.