According to the World Health Organization, about 13.4 million infants are born premature each year (gestational age, GA < 37 weeks). Due to organ immaturity, these infants face increased risks of complications, comorbidities, and altered development, leading to immediate and long-term health problems. Sleep is a key indicator and regulator of their developmental and maturational trajectories. Among the three sleep states in premature infants, quiet sleep is particularly important, as it supports the maturation of memory-related brain regions and the establishment of long-range functional connectivity. By analyzing physiological signals, namely heart rate, respiration rate, and ECG-derived motion, this work aims at the detection of periods without movements, called quiet periods (QP), and their temporal patterns to inform the development of premature infants.