How much should my baby weigh? Is my baby growing enough? Am I feeding them enough? These are among the most common questions in the first year of life, and the anxiety around growth is particularly acute because weight gain is visible and measurable in a way that other aspects of development are not. Growth charts help contextualise weight within the range of normal human variation, but they can also generate unnecessary anxiety if misinterpreted.
Healthbooq (healthbooq.com/apps/healthbooq-kids) covers newborn health and infant growth monitoring in the early months.
Normal Weight Loss After Birth
Almost all newborns lose weight in the first days after birth. This is a normal physiological phenomenon, not a sign of inadequate feeding (though inadequate feeding can worsen it). The mechanisms include loss of meconium (the first stools), fluid shifts as the baby adapts to extrauterine life, and the relatively low volume of colostrum in the first days before mature milk comes in.
The NHS expectation is that newborns may lose up to 7-10% of their birth weight in the first week. Weight loss exceeding 10% of birth weight should trigger a feeding assessment. Most babies should regain their birth weight by day 10-14; failure to regain by day 14 warrants further assessment of feeding and potentially medical review.
Expected Weight Gain
After regaining birth weight, the typical pattern of weight gain is:
0-3 months: approximately 150-200g per week (around 30g per day). This is the most rapid period of weight gain in a child's life relative to body size.
3-6 months: approximately 100-150g per week. Growth rate begins to slow.
6-12 months: approximately 70-90g per week. Weight gain continues but at a slower pace.
1-2 years: approximately 2-3 kg over the whole year.
These are population averages; healthy individual babies vary considerably. A breastfed baby may gain weight less predictably and in more "lumpy" patterns than a formula-fed baby; there may be weeks of rapid gain and weeks of slower gain that average out normally over time.
How Growth Charts Work
The UK uses the UK-WHO growth charts, which are based on the WHO Child Growth Standards derived from a study of breastfed children raised in optimal conditions in six countries. These charts show centile lines: the 50th centile is the median (half of healthy children fall above, half below); the 2nd and 98th centiles represent the extremes of the normal range. A baby on the 2nd centile – which is the 2nd percentile from the bottom – is at the lower end of normal but is small, not failing to thrive.
The most important principle in reading a growth chart is consistency: a baby following their own centile trajectory, whether on the 9th or 91st centile, is growing normally. What matters clinically is not where on the chart a baby is but whether they are following a consistent line.
Centile crossing – moving from one centile band to another on the chart – is clinically significant when it crosses two or more centile bands downward. Some modest centile variation is expected and normal; a premature baby may "catch up" by crossing upward in the first months; a large baby may settle down toward a more genetically appropriate centile. But sustained downward crossing of two or more centile lines in a previously well baby warrants clinical review.
Failure to Thrive
"Failure to thrive" (more recently termed "faltering growth" in UK clinical practice) describes inadequate weight gain over time relative to expected patterns. It has multiple possible causes: inadequate intake (feeding difficulties, low supply, feeding relationship problems), inadequate absorption (coeliac disease, inflammatory bowel disease, food allergy), or increased metabolic demand (chronic illness, cardiac disease). Assessment by a health visitor and, where needed, a GP or paediatrician is appropriate for any baby whose growth is not following expected patterns.
The majority of cases in the UK have non-organic causes (feeding difficulties, low supply) rather than underlying medical conditions, and respond to feeding support. Early identification and intervention is associated with better outcomes.
Key Takeaways
All newborns lose weight in the first days of life – up to 7-10% of birth weight – and most regain their birth weight by 10-14 days. After regaining birth weight, typical weight gain is approximately 150-200g per week in the first 3 months, slowing to 100-150g per week from 3-6 months and around 70-90g per week from 6-12 months. Growth is assessed on UK-WHO growth charts using centile lines. A baby following a consistent centile trajectory is growing normally even if they are on the 2nd centile. Crossing two or more centile lines downward warrants clinical assessment.
