Objective. To evaluate the potential relation between body position and sleep characteristics in normal infants.

Patients. Two groups of 3-month-old healthy infants were evaluated: 40 infants who usually slept supine, and 40 who usually slept prone. The two groups were matched for gender, gestational age, postnatal age, birth weight, and total recording time.

Recording techniques. The 80 infants were studied polygraphically during one night in the pediatric sleep laboratory. They were allowed to fall asleep in their usual sleep position, and every 3 hours were gently turned from prone to supine, or from supine to prone.

Results. In each group, 6 infants were excluded from the analysis, because they woke up after having been turned over. In both groups, no significant difference was seen between the prone and the supine body positions for the following variables: number of sleep state changes; number of gross body movements; percent of rapid eye movement sleep; saturation with oxygen, arterial blood levels; number and duration of acid esophageal reflux; rectal temperature; mean respiratory rates; water evaporation rates from the forehead skin; and number or duration of central or of obstructive apneas. In both groups of infants, prone body position was associated with a significant increase in sleep duration (+ 6%) and in non-rapid eye movement sleep (+25%) and a significant decrease in number of arousals (–40%) and in their duration (–43%).

Conclusions. No explanation has been found for the sleep-promoting effect of prone body positioning. The finding could be of interest to the study of infants' sleep quality, as well as to the potential relation between body positions and sudden death during sleep.

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