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Fluid, not failure: Understanding your baby’s first weight changes.
Why babies often “lose weight” after birth (and why it’s not always a problem).
Many babies look like they “lose weight” in the first few days after birth. In lots of cases, that early drop is mostly about fluid shifts, not a true loss of body tissue, and it can be more pronounced after caesarean, epidural, and higher volumes of IV fluids in labour.
If we mistake normal fluid diuresis for poor feeding, families can be pushed toward unnecessary top-ups with formula. What matters is skilled feeding assessment, not the scale number alone, and why it might be better to weigh baby after 24 hours from birth, not immediately after birth.
Sadly, breastfeeding is often undermined in the very first days after birth. Many parents are told their baby “needs more” when in fact their tiny tummy is only designed to take a small amount at a time. Instead, some babies are topped up with 30 mL or more of artificial formula, stretching their stomachs and disrupting the natural rhythm of feeding and digestion. This isn’t the fault of the parents, it’s because the system doesn’t always support them with accurate, evidence-based information. A common belief is that every paediatrician or midwife is fully trained in breastfeeding management, but this is a huge misconception. While most clinicians have a basic understanding, few receive in-depth lactation education. That’s why access to qualified lactation consultants (IBCLCs) and breastfeeding counsellors is so important. With the right guidance, parents can trust their instincts, feed according to their baby’s cues, and avoid unnecessary interventions that can make breastfeeding harder.
What newborn weight changes really reflect
All babies shed fluid after birth as they move from life inside the uterus to independent fluid balance. Passing urine and meconium contributes to an initial fall on the scales, with a typical low point around 48 – 72 hours of life.
The Australian Breastfeeding Association (ABA) explains that breastfed babies commonly lose up to 10% of their birth weight in the first week and are expected to regain their birth weight by about 2 weeks. ABA also highlights the importance of looking at trends over time rather than reacting to a single weight check.
Read more here:
https://www.breastfeeding.asn.au/resources/weight-gains
An observational study followed healthy, breastfed babies and found that the amount and timing of maternal IV fluids were associated with increased neonatal output (more wees / poos in the first 24 hours) and a bigger early weight drop. The authors concluded that babies appear to diurese (shed excess water) in that first day and advised clinicians to consider the 24-hour weight as a more meaningful baseline than the delivery-room weight, especially when large IV volumes were given.
Read the study here:
https://internationalbreastfeedingjournal.biomedcentral.com/articles/10.1186/1746-4358-6-9
Why this matters more after caesarean and epidural
Planned caesarean births and epidurals commonly involve pre-loading with IV fluids to stabilise blood pressure. That extra fluid can inflate the baby’s “birth weight” number and set the stage for a larger apparent loss as the baby pees out the excess in the first day or two. Multiple studies link epidural use, higher maternal IV fluid rates, and delayed secretory activation (lactogenesis II) with a higher likelihood of “excess” early weight loss on paper.
It’s also true that caesarean birth is a risk factor for delayed milk coming in (lactogenesis II after 72 hours), due to factors like surgical stress, blood loss, and later first feeds. That can compound the picture and does deserve extra feeding support, again, through assessment, not just automatic formula orders.
Not all studies agree, and one paediatric study in caesarean births didn’t find a dose response relationship between the exact type / amount of intrapartum fluid and “excess” neonatal loss, reminding us that weight trajectories are multifactorial (labour course, timing of feeds, clinical practices, etc.). The sensible takeaway is to not hang everything on one number but look at the whole baby and the whole feeding picture.
https://bmjpaedsopen.bmj.com/content/bmjpo/1/1/e000070.full.pdf
What counts as “normal” early weight loss?
When assessing feeding and output in the first few days, it’s more accurate to think in hours, not just “Day 1” or “Day 2.” A baby who is 30 hours old is very different from a baby who is 10 hours old. In the first 24 hours, we only expect one wet nappy, as babies are still adjusting to life outside the womb and taking in small amounts of colostrum. If a newborn is passing more urine than expected, particularly after the mother has received a lot of IV fluids during labour, it can be a sign that the baby is flushing out that extra fluid rather than losing “real” weight. This is another reason why using the 24-hour weight as a baseline is more meaningful than the delivery-room weight and why careful observation over time tells a far clearer story than one number on a scale.
There are growth charts (like the NEWT tool) that track how babies’ weight changes hour by hour in the first few days. These charts are based on thousands of healthy, breastfed babies and show what’s typical, so parents and care providers don’t worry when a baby’s weight follows a normal pattern. In general practice, many services consider ~7% a point for closer review, and ≥10% a red flag for full assessment, NOT an automatic reason to formula-feed.
The ABA supports this by noting that some weight loss is expected but stresses the importance of clinical context and monitoring overall health, output, and feeding cues. In their “First Week” resource, they specifically caution that formula top-ups given too quickly can make it harder to establish breastfeeding, as the baby spends less time at the breast and the mother’s milk supply is not stimulated as effectively.
See ABA’s first week resource here:
https://www.breastfeeding.asn.au/resources/first-week
The real risk with knee-jerk top-ups
Early, unnecessary formula top ups “just to be safe” can kick off a supplementation spiral: less time at the breast, less milk removal, slower milk supply, and more top-ups. The Academy of Breastfeeding Medicine (ABM) which is a group of doctors who specialise in breastfeeding care, says that most healthy, full-term babies do not need extra milk (formula or expressed milk) unless there’s a genuine medical reason. Supplementing should only happen after a proper breastfeeding assessment by someone who really understands feeding, such as a lactation consultant.
When supplementation is indicated (e.g., signs of dehydration, persistent hypoglycaemia unresponsive to feeding, significant hyperbilirubinemia, or truly excessive / ongoing loss with poor transfer), ABM recommends prioritising expressed breast milk, using small, physiologic volumes, and preserving breastfeeding with skin-to-skin and frequent milk removal.
The ABA echoes this approach, encouraging parents and health professionals to seek breastfeeding support first and avoid rushing into formula unless there’s a genuine medical reason formula is required.
A practical way to read the scales wisely
If labour involved large IV fluid volumes, epidural, induction / augmentation, or a caesarean, consider these points with your health care providers:
What women and partners can do
Why colostrum is the best top-up
If a baby does need a little extra in the early days, colostrum is always the first choice. Colostrum is the thick, golden first milk your body produces before mature milk comes in. Even tiny drops are packed with:
Hand-expressed colostrum can be collected after birth and offered to the baby by syringe, spoon, or cup. Some women also choose to express and store colostrum antenatally, so they have it ready should their baby need extra support in the first days.
Unless there is a genuine medical reason for formula, colostrum is always preferable for topping up a newborn as it gives the baby all the benefits of breastmilk while supporting the mother’s milk supply at the same time.
More interesting facts about colostrum
Birth educator Pip Wynn Owen from Birth Savvy Bub Savvy has highlighted new research showing just how powerful colostrum can be in protecting babies from food allergies. In her blog “Colostrum Protects Against Food Allergies”, she explains that exclusive colostrum feeds in the first 72 hours of life significantly lowers the risk of allergies such as peanut, egg, and cow’s milk. This is because colostrum coats and strengthens the newborn’s gut lining while delivering immune-boosting cells and antibodies, giving babies an important layer of protection right from the start.
Click here to read more: https://birthsavvy.com.au/colostrum-protects-against-food-allergies/
And picture how small your baby’s tummy is in those early days:
Day 1: ~ 5–10 mL (≈ the size of a cherry)
Day 2: ~ 10–15 mL (≈ the size of a grape)
Day 3: ~ 22–30 mL (≈ walnut size)
Days 4–7: ~ 30–60 mL (≈ apricot size)
Week 2–3: ~ 60–90 mL (≈ egg size)
A note about the images you may see: Many charts and infographics (including the fruit-size ones) show a “stomach” drawn on a baby’s belly for teaching purposes. This is a visual tool only, to help parents understand volume capacity. Anatomically, a newborn’s stomach actually sits much higher, just under the diaphragm and mostly on the left side beneath the ribs, at about nipple-line level. In babies, the stomach is also more vertical in shape compared to older children and adults. So while the diagram helps families see why small, frequent feeds are normal, it’s not a precise anatomical placement of the stomach.
So to summarise, it’s normal for babies to lose a little weight in the first few days after birth. In most cases, this isn’t a sign of poor feeding or low milk supply, but rather a natural release of extra fluid, especially if the mother has had IV fluids, an epidural, or a caesarean birth. What matters most is how the baby is feeding, weeing, pooing, and behaving, not a single number on the scale.
Care providers should look at the whole picture before suggesting formula top-ups, and parents can feel confident knowing that colostrum is the best supplement in the early days if extra milk is needed. Even the smallest drops are powerful, providing antibodies, immune protection, and nourishment perfectly designed for a newborn’s needs.
With gentle feeding support, regular skin-to-skin contact, and time, most babies quickly regain their birth weight and thrive. The first few days are all about learning, adjusting, and trusting the beautiful design of the body: one feed, one cuddle, and one tiny tummy at a time.
References:
Noel-Weiss J. et al. Maternal fluids during parturition, neonatal output, and breastfed newborn weight loss. International Breastfeeding Journal, 2011.
https://internationalbreastfeedingjournal.biomedcentral.com/articles/10.1186/1746-4358-6-9
Chantry C. et al. Excess weight loss in first-born breastfed newborns… Paediatrics, 2011.
https://pubmed.ncbi.nlm.nih.gov/25554815/
Flaherman V. et al. Early weight-loss nomograms for exclusively breastfed newborns. Paediatrics, 2015.
https://publications.aap.org/pediatrics/article-abstract/135/1/e16/52890/Early-Weight-Loss-Nomograms-for-Exclusively?redirectedFrom=fulltext
ABM Clinical Protocol #3: Supplementary feedings in the healthy term breastfed neonate (2017).
https://www.bfmed.org/assets/DOCUMENTS/PROTOCOLS/3-supplementation-protocol-english.pdf
BMJ Paediatrics Open. Intrapartum IV fluids for caesarean and newborn weight loss (2017).
https://pubmed.ncbi.nlm.nih.gov/29637114/
South Eastern Sydney LHD. Weight loss in breastfed neonates – assessment & management (policy).
https://www.seslhd.health.nsw.gov.au/sites/default/files/documents/weightlossbreastfed19.pdf
NSW Royal Hospital for Women LOP. Day 4–6 weight loss >10% (management plan).
https://www.seslhd.health.nsw.gov.au/sites/default/files/documents/weightlossbreastfed19.pdf
Australian Breastfeeding Association: Weight gains and the first week
https://www.breastfeeding.asn.au/resources/first-week
If you have any questions or would just like more information please don't hesitate to get in touch by clicking the button below and filling out the contact form.
Contact Vicki