Babies do not grow at one steady speed. A few days of more frequent feeding, different sleep or fussiness may happen alongside growth, but behaviour alone cannot prove a 'growth spurt'. The reliable picture comes from weight, length and head-circumference measurements reviewed over time.
Growth is measured as a trend
WHO standards help clinicians plot measurements by age and sex. One home weight or a difficult week does not show a leap or a growth problem. Accurate measurements and the shape of the curve matter more.
Wonder Weeks is not an official timetable
WHO growth standards do not include a calendar in which every baby has the same mental leap in the same week. One small study found that bursts of increased sleep and length growth sometimes occurred close together; it did not establish universal, predictable weeks.
Track what helps the conversation
For a few days, note feeds, sleep, wet diapers and the change you noticed. Do not restrict or increase milk solely because an online leap calendar says you should; discuss feeding concerns with the professional who follows your baby.
When to contact a clinician
Do not wait under the label of a growth spurt if your baby is refusing feeds, has clearly fewer wet diapers, repeatedly vomits, seems unusually sleepy or you are worried about weight gain. Call 911 in the US or 999 in the UK for breathing trouble, blue or grey skin, a seizure or difficulty waking.
Related guides
Use the country-specific guides to review feeding, sleep and development in the first months.
View references and primary sources
- World Health Organization — Child Growth Standardsaccessed September 2026
- Sleep — Infant sleep and length growth study1 May 2011 · accessed September 2026