'Four-month sleep regression' is a common description, not a medical diagnosis or a phase with a fixed start and finish. Sleep organisation changes during early infancy, but babies do not all become unsettled at the same age or for the same length of time.

01

What may be changing?

Day and night become more distinct, sleep cycles mature, and babies may wake more visibly between cycles. Feeding, illness, growth, stimulation and new skills can also change sleep. The label describes what you see; it does not identify the cause.

02

Keep the response simple

Use a calm, repeatable bedtime routine and offer age-appropriate chances to settle.

Do not chase a perfect schedule after one difficult night.

If tracking helps, note when the change began and look at several days together.

03

Safe sleep rules do not change

Place your baby on their back on a firm, flat sleep surface with no pillows, loose bedding, toys or positioners. Do not use weighted sleep products. A monitor or tracking app cannot make an unsafe sleep space safe.

04

Use the record, not the label

A short record of sleep, feeds and diapers can show whether the change is isolated or part of a wider pattern.

05

When to ask for help

Contact your clinician if the change comes with poor feeding, fewer wet diapers, fever, persistent vomiting or unusual drowsiness. For breathing trouble, blue or grey skin, a seizure or difficulty waking your baby, call 911 in the US or 999 in the UK now.

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