Breastfed newborns commonly lose some weight in the first days, usually reaching their lowest point around day 3 to 4 and regaining birth weight by about two weeks. Loss of more than about 10% of birth weight, or failure to start regaining by day 5, warrants a full feeding assessment.
Large losses can come with hypernatraemic dehydration, which may look deceptively well until it is severe. Weigh the baby, check urine and stool output, observe a feed, and check serum sodium if weight loss is excessive.
- Weigh newborns at the early postnatal review and compare with birth weight.
- Treat loss over about 10% of birth weight as a trigger for a feeding assessment.
- Check serum sodium when weight loss is excessive or the baby is lethargic.
- Count wet and dirty nappies; fewer than expected is an early warning.
- Support breastfeeding first; supplement when clinically needed, not as a reflex.
Why it matters
Hypernatraemic dehydration in breastfed newborns is preventable, and a scale at the early review is the cheapest test for it.
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