In plain words
An ultradian cycle is a rhythm that repeats more than once within a day. In babies, sleep follows a cycle of roughly 50 to 60 minutes, with light and taking turns. Adults cycle about every 90 minutes. Because a baby's cycle is short, she moves toward lighter sleep many times a night and wakes more easily between cycles. Feeding and comfort help her settle again. The cycle is a normal part of development, not a sign that something is wrong. It becomes longer and more adult-like over the first year, and that is part of why night sleep improves over time.
The deeper version
Infant sleep is organized into active (REM-like) and quiet (non-REM-like) states that alternate on a cycle of approximately 50 to 60 minutes in term newborns, compared with about 90 minutes in adults. The cycle lengthens across the first months as cortical and brainstem sleep regulation mature (Anders and Keener 1985). Within each cycle, transitions into lighter sleep carry a higher arousal likelihood, which underlies the frequent night wakings of early infancy. The consolidation of nocturnal sleep typically emerges between 3 and 6 months.
Where it comes up
- Breastfeeding and sleep: feeding to sleep, night feeds, and sharing the loadFeeding Your Baby
- Days and nights mixed upBaby Basics
- Newborn sleep and safe sleepBaby Basics
- Sharing nights: shifts and systemsSupport, Home, and Village
What mothers here say about ultradian cycle
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Sources
- Anders TF, Keener MA — Developmental course of nighttime sleep-wake patterns in full-term and premature infants during the first year of life. Sleep 1985
- Iglowstein I et al. — Sleep duration from infancy to adolescence: reference values and generational trends. Pediatrics 2003