In plain words
A circadian rhythm is the internal clock that runs about one day long and controls sleep, appetite, body temperature, and hormone release. Newborns do not have a mature rhythm yet. Their sleep comes in short stretches around the clock, and the rhythm develops over the first months. Daylight exposure during the day and dark, quiet nights help the rhythm set. Mothers often notice this as a baby who sleeps most of the day and is alert at night. The rhythm also shifts for mothers after birth, because hormones change and sleep is broken. Some mothers report that light and routine seem to help both of them.
The deeper version
The suprachiasmatic nucleus entrains peripheral clocks through light input via the retinohypothalamic tract, and secretion is a robust marker of rhythm. In infants, melatonin production matures over the first three to four months. Rivkees (2003, Pediatrics) described the developmental trajectory of infant circadian organization and the role of light in entrainment. Harrison (2004) reported that afternoon light exposure was associated with better nighttime in six- to twelve-week-old infants. Sleep fragmentation in new mothers has been associated with mood symptoms and reduced daytime function, which is why postpartum circadian disruption is part of perinatal sleep research. The main controversy concerns whether deliberate light and schedule interventions meaningfully shorten the period of night waking.
Where it comes up
- Days and nights mixed upBaby Basics
- Sleep deprivation: what it does and how to survive itPostpartum: Your Body
- Night weaningFeeding Your Baby
- Sharing nights: shifts and systemsSupport, Home, and Village
- Fussy weeks and developmental changesBaby Basics
- Leaving the house for the first timeSupport, Home, and Village
What mothers here say about circadian rhythm
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Sources
- Rivkees SA — Developmental physiology of circadian rhythms in infants. Pediatrics 2003
- American Academy of Pediatrics — Recommendations for prevention of sudden infant death syndrome, 2022