Newborn guides

Newborn weight loss after birth: what's normal?

Almost all babies lose a little weight in the first few days — it’s expected, not a warning sign. Most lose weight until around day 3 or 4, then start gaining, and most are back to their birth weight by about 3 weeks. A loss of up to about 7% of birth weight is considered normal.

Why newborns lose weight at first

Babies are born with extra fluid, and they pass this in their first wees and poos (the black, tarry meconium). In the first couple of days breastfed babies take small amounts of colostrum — rich but low in volume — before your milk “comes in” around day 3–4. So a small dip is simply your baby shedding fluid faster than they’re taking milk on board. It levels off quickly.

How much weight loss is normal?

• Up to ~7% of birth weight: within the usual range. Keep feeding well and keep an eye on nappies.
• More than 7%: worth mentioning to your midwife the same day. They’ll usually watch feeding and may weigh again sooner.
• 10% or more: needs a feeding assessment and review without delay — contact your midwife or doctor now. It doesn’t necessarily mean anything is seriously wrong, but it should be checked promptly.

Percentages are worked out from birth weight. For example, a baby born at 3,500 g losing 7% would be about 3,255 g; a 10% loss would be about 3,150 g.

When should they be back to birth weight?

The NHS guide is by about 3 weeks (day 21). Some babies get there sooner, around 10–14 days; others take the full three weeks. After that, a rough guide for healthy gain is about 150–200 g a week in the early months, though babies grow in fits and starts rather than a straight line. If your baby hasn’t regained birth weight by 2 weeks, your midwife or health visitor will keep a closer eye and support feeding.

How weight is tracked in the UK

Your baby is weighed at birth, and again around day 5 and day 10 by your midwife, then by your health visitor. Weights are plotted on the UK-WHO growth charts in your red book (the Personal Child Health Record). What matters is the trend along a centile line, not a single reading — and babies aren’t expected to weigh in more than once a week or two once feeding is established, because frequent weighing just adds noise and worry.

Weigh on the same scales where you can, with your baby undressed, and remember that a full bladder, a recent feed or a big poo can shift the number by 100 g or more.

A weight “line” tells you far more than any single number, but only if you can see it. Beanlo plots each weigh-in against the WHO centile for your baby’s age and sex, so you can watch the trend between health visitor visits instead of guessing from one reading.