How much weight does a newborn lose after birth, and why?
Weight loss in the first days of life is physiological. The Academy of Breastfeeding Medicine (ABM) explains that after moving from life in the womb to life outside it, a newborn passes excess extracellular fluid and meconium, so they get lighter. The UK's NICE adds that the loss usually stops after about 3-4 days, and the NHS says the baby should then start gaining weight steadily.
In a study cited by the ABM, at a hospital with good feeding support, exclusively breastfed babies lost 5.5% of their birth weight on average, but more than one in five lost over 7%. Losses are usually larger after a caesarean. In a study of over 160,000 healthy breastfed newborns, almost 5% of vaginally born babies and over 10% of babies born by caesarean had lost 10% or more of their birth weight by 48 hours, and by 72 hours this applied to over 25% of babies born by caesarean.
You can work out the percentage yourself: subtract the current weight from the birth weight, divide the result by the birth weight and multiply by 100. For example, a baby born weighing 3500 g who weighs 3220 g on day 3 has lost 280 g, which is 8% of their birth weight.
| Loss of birth weight | What guidance says | What to do |
|---|---|---|
| Up to about 7% | Below the level Medycyna Praktyczna treats as needing attention (the average loss in breastfed babies is about 5.5%) | Feed often, keep an eye on nappies and how the baby behaves |
| More than 7% | Medycyna Praktyczna treats this as a situation needing particular attention, but not immediate supplementing | Ask a midwife to assess the feeding |
| 8-10% from day 5 of life | According to the ABM this may still be within normal limits if everything else is fine, but it needs careful assessment | Assessment of the baby and the feeding, with breastfeeding help if needed |
| More than 10% | NICE recommends examining the baby for dehydration and illness, a detailed feeding history and watching a feed | Contact a midwife or doctor promptly |
When does a newborn regain their birth weight?
Sources give slightly different timings, but they describe the same window. The American Academy of Pediatrics (AAP) says babies start gaining weight steadily from about 5 days old and should be back at their birth weight by about 2 weeks, with almost all babies regaining it by 3 weeks. In a study cited by the ABM, breastfed babies were back to birth weight after 8.3 days on average, and 97.5% of them had regained it by day 21.
Medycyna Praktyczna, a Polish medical publisher, lists not regaining birth weight within 2 weeks among situations needing particular attention. NICE and the NHS say most babies are back to birth weight by 3 weeks. The NHS notes that babies are weighed during the first 2 weeks precisely to check that they are regaining their birth weight. If a baby has not regained it by 3 weeks or has lost a lot of weight, a midwife talks to the parents about feeding, may watch a breastfeed and looks at the baby's health in general.
How much weight should a breastfed newborn and baby gain?
Weight gain is counted from the lowest weight after birth, not from the birth weight. This is the advice of lactation consultant Dr Magdalena Nehring-Gugulska in Medycyna Praktyczna, who gives an example: a baby born weighing 3700 g weighed the least on day 3, 3460 g, and 3820 g on day 12. So the baby gained 360 g in 9 days, an average of 40 g a day.
Medycyna Praktyczna gives Professor Ruth Lawrence's norms as the closest to the WHO charts. According to them, a breastfed baby gains:
- 26-31 g a day from 0 to 3 months, which works out at roughly 180-220 g a week,
- 17-18 g a day from 3 to 6 months,
- 12-13 g a day from 6 to 9 months,
- 9 g a day from 9 to 12 months.
The AAP gives an average gain of almost 28 g a day for the first month. Babies double their birth weight at 5-6 months. The WHO also publishes standards for weight gain month by month. The table shows the median, the middle value, and the range from the 15th to the 85th centile, which covers 70% of healthy babies. Gain in the first 4 weeks is counted from birth weight, so it also includes the physiological loss.
| Baby's age | Gain per month: girls, median (15th-85th centile) | Gain per month: boys, median (15th-85th centile) |
|---|---|---|
| 0-4 weeks | 879 g (602-1171 g) | 1023 g (681-1336 g) |
| 4 weeks to 2 months | 1011 g (734-1301 g) | 1196 g (886-1524 g) |
| 2-3 months | 718 g (494-952 g) | 815 g (577-1071 g) |
| 3-4 months | 585 g (376-804 g) | 617 g (403-845 g) |
| 4-5 months | 489 g (286-703 g) | 522 g (311-746 g) |
| 5-6 months | 401 g (203-611 g) | 422 g (217-640 g) |
According to the NHS, babies gain weight most rapidly in the first 6 months, and the rate then gradually slows down. When a baby is ill, weight gain may slow for a while and usually returns to normal within 2-3 weeks.
How can you tell a breastfed baby is getting enough milk?
Breasts have no measuring scale, but the NHS lists signs that together show well whether a baby is getting enough milk:
- The feed starts with a few rapid sucks, followed by long, rhythmic sucks and swallows with occasional pauses.
- You can hear and see your baby swallowing, and their cheeks stay rounded, not hollow, during sucking.
- Your baby is calm during the feed, comes off the breast on their own at the end and seems content and satisfied after most feeds.
- Your breasts feel softer after feeds, and your nipple looks more or less the same as before, not flattened or white.
- When awake, your baby looks healthy and alert.
Nappies are the second objective sign. According to the NHS, in the first 48 hours a baby usually has only 2-3 wet nappies. From day 5 wet nappies should become more frequent, up to at least 6 heavy, wet nappies every 24 hours. From day 4 the baby should also do at least 2 soft, yellow poos a day for the first few weeks. It can be hard to tell whether disposable nappies are wet, so the NHS suggests adding 2-4 tablespoons of water to a dry nappy to see what a wet one looks and feels like.
How often the baby feeds matters too. The Polish standard of perinatal care notes that in the early days of breastfeeding a baby is put to the breast up to a dozen or more times a day. A newborn who does not wake on their own should be woken for a feed 3-4 hours after the start of the last feed. The exception is the first day of life, when waking is not required.
When is weight loss a reason to get help quickly?
Do not wait for the next planned visit. Contact a midwife or doctor if:
- your baby has lost more than 10% of their birth weight, because NICE then recommends examining the baby and watching a feed,
- they have not regained their birth weight within 2 weeks, and especially if they have not done so by 3 weeks,
- from day 5 they have fewer than 6 heavy nappies a day, or wet nappies suddenly become fewer,
- they do few poos: the ABM lists fewer than 4 stools on day 4, or meconium stools still on day 5, among the signs of not getting enough milk,
- they gain clearly less than the norms, or their curve on the centile chart has dropped by two centile channels.
Contact a doctor urgently, and if the baby seems seriously unwell, go to the SOR (hospital emergency department) or call 112, if your baby is lethargic, very hard to wake for feeds or is hardly feeding at all. The ABM lists poor feeding and lethargy among the signs of significant dehydration, which needs a doctor's assessment.
How should you weigh a newborn and read WHO centile charts?
Medycyna Praktyczna advises placing the scale on a flat, hard surface, putting a nappy on it and zeroing the scale, then weighing the baby without clothes and without a nappy. If you compare results from several days, weigh at the same time of day. The most common mistakes are a scale on a soft or uneven surface, weighing in clothes, a wriggling baby, a weak battery in the scale, miscounting the days and comparing the result with birth weight instead of the lowest weight.
Weighing every day at home is usually not needed. Even when a baby has lost more than 10% of their birth weight, NICE recommends weighing them no more often than once a day, at intervals depending on the level of concern. After the first 2 weeks, the NHS advises weighing a baby no more than once a month up to 6 months and no more than once every 2 months from 6 to 12 months. Babies are weighed more often if parents ask or if there are concerns about their health or growth.
A centile chart is a graph on which the baby's weight is plotted over the weeks and months. The centile lines show how healthy children usually grow. The 50th centile line is the middle: half of babies of that age weigh less and half weigh more. The WHO standards from 2006 were based on measurements of 8,840 children from 6 countries who were exclusively breastfed for 4-6 months, which is why Medycyna Praktyczna recommends them for assessing breastfed babies. Medycyna Praktyczna has also pointed out that older Polish charts in child health books, developed in 1999, were based on data from mostly formula-fed babies, who tended to grow faster.
The direction of the curve matters more than the centile itself. According to the NHS, a baby's weight may go up or down by one centile line, but crossing two lines is less common and worth discussing. NICE treats a fall across two or more spaces between centile lines, in babies whose birth weight was between the 9th and 91st centile, as a reason to assess growth. According to NICE, the position on the chart alone is a cause for concern only when the baby's weight is below the 2nd centile.
How does a midwife help with poor weight gain, and when should you supplement?
After the birth, a primary care (POZ) midwife makes at least 4 free home visits under the NFZ, Poland's public health insurer, the first within 48 hours of being notified of the birth, not counting Saturdays, Sundays and public holidays. Under the standard of perinatal care she weighs the baby at these visits and assesses weight gain or loss. She also checks how often and how long the baby feeds, whether they suck willingly and seem satisfied, assesses the mother's breasts and the baby's mouth, the feeding technique and how effectively the baby sucks. If a problem goes beyond her competence, she tells you that a doctor needs to be consulted.
Watching a feed is an important part of the assessment. NICE recommends that when a baby has lost more than 10%, feeding is observed by a person with appropriate training in breastfeeding and bottle feeding. With longer-lasting problems, a CDL lactation adviser or an IBCLC lactation consultant can help. We explain how their help differs from a midwife's in a separate article.
Supplementing is a decision best made together with a midwife, lactation adviser or doctor, after assessing the baby and the feeding. The ABM stresses that a 10% loss is not an automatic reason to supplement but a reason to assess the baby, and that most breastfed babies do not need supplementing. NICE points out that supplementing with formula may help with weight gain but often results in breastfeeding stopping.
If supplementing is needed, the ABM names the mother's expressed milk as the first choice and, if there is not enough of it, donor human milk. NICE recommends that when formula is given, the mother is supported to continue breastfeeding, expresses milk to keep up her supply and gives the baby any available breast milk first. In hospital, under the Polish standard of perinatal care, formula is given on a doctor's order and in line with the mother's decision after she has been counselled, and the method of supplementing is chosen so that it does not make breastfeeding harder.
If you would like someone to watch a feed and weigh your baby outside the patronage visits too, you can book a private home visit from a midwife with lactation experience.
