Baby's Weight Gain in the First Year

By: Sabrina Granniss, IBCLC


6 min

Your baby’s weight gain and making enough milk are two of the top concerns new parents have. Many factors influence your baby’s weight loss immediately after birth and their growth during the first couple weeks and beyond.

Overview of your baby’s growth

  • Babies lose an average of 5 - 7% of their birth weight in the first few days after birth (2)
  • Losing up to 10% of their birth weight is considered acceptable
  • Baby’s weight at 24 hours old may be a more accurate representation of true birth weight
  • Babies lose the most weight in the first 2 days after birth (2)
  • Your baby should regain their birth weight by the time they are 2 weeks old
  • During the first 3 months, your baby will gain about 1 ounce per day
  • By 4 months old, your baby will double their birth weight
  • From ages 6 - 12 months old, your baby will gain about 3 - 5 ounces per week
  • Your baby will triple their birth weight by about 1 year old
  • Boys gain weight faster than girls
  • Babies grow about 10 inches in length during the first year of life (4)

Growth charts

The United States began using growth charts in 1977. It can be one tool in measuring the growth of your baby. Growth charts are not reflective of your baby. The World Health Organization growth charts show patterns of growth that are the standards for how a baby should grow. They were created by looking at the growth pattern of babies who predominantly breastfed for at least four months and were still breastfeeding at twelve months. (1) Babies' differences must be considered when determining appropriate and acceptable weight gain. Your baby’s length and head circumference should be considered as part of looking at their growth in addition to weight.

How to Read a Growth Chart

  • Percentile - this shows a measurement of your child’s weight compared to other children the same age.
  • Z-score - the standard deviation above or below the mean. It tells you where your baby’s score is on the curve. For example, a z-score of zero means your baby’s weight is exactly average or 50%. A score of +3 means your baby is above the average, and -3 is below the average.
  • Growth curve - It is important not to look at just the numbers alone. Remember, your baby is unique and an individual. They should follow their curve, meaning if they are in the 30th percentile, they should continue to chart at the 30th percentile. Knowing what percentage your baby falls into can be helpful, but it shouldn’t be the only consideration. If your baby is not following their curve or is dropping percentiles, this can be cause for concern, and you should meet with your IBCLC (International Board Certified Lactation Consultant) to figure out why and how to help your baby gain weight.

Signs your baby is gaining weight

Between visits to the care provider where your baby gets weighed, you can gauge how well your baby is doing by the listed signs of growth and weight gain below.

  • Your baby looks bigger - as they grow, you see them look more rounded in their cheeks and legs, and other areas of their body are filling out.
  • They have plenty of wet diapers per day - your baby should have one wet diaper for each day they are old until your milk transitions from colostrum to more volume, and by day 5, your baby should have at least 6-8 or more wet diapers. A wet diaper means it is full, not just lightly damp. To know what this looks and feels like, pour 3 Tablespoons of water on a clean, dry diaper for reference. Suppose you are not seeing enough pee diapers or there are orange-colored crystals in your baby’s diaper. In that case, this is a sign of dehydration, and you should call your pediatrician immediately.
  • Poop diapers - after day 4, your baby should have 3-4 or more poop diapers per day. The amount of poop should be at least the size of a quarter. It should be soft yet have substance rather than be liquidy. 
  • Your baby seems relaxed and content after nursing.
  • Your breasts may feel more full before feeding and less full after feeding.
  • Your baby has a rhythm of nursing, sleeping, and some alert time and is mostly happy and content.
  • Your baby rouses to feed every 2-3 hours on their own.
  • Your baby detaches themself when they are done nursing and seems satisfied.
  • Your baby takes up more space in the car seat or bed. 
  • They are growing out of their clothes.

Keeping on track

  • Follow your baby’s cues for feeding - expect to breastfeed every 1.5-3 hours around the clock.
  • Middle-of-the-night nursing is essential for you and your baby. Prolactin levels are highest at night, and milk removal during this time significantly influences overall milk production. Babies get around 30% of their calories during middle-of-the-night feedings. It is normal for babies to wake during the night, even well past one year old.
  • During a growth spurt, offer your milk more often, still following your baby’s cues. Growth spurts are expected at 7-10 days, 2-4 weeks, 6-8 weeks, 3 months, 4 months, 6 months and 9 months old. (5) 
  • Always give breast milk before solid foods after introducing solids sometime around 6 months of age. Solid foods are complementary to breast milk and should not be given first or in place of breast milk.
  • Spend time skin-to-skin with your baby as much as possible while breastfeeding is being established and continue lots of contact with your baby as they grow by babywearing in a sling you can nurse in, taking baths together, learning infant massage, and continuing time skin-to-skin.

What can interfere with weight gain?

  • Medications taken during labor - some medicines can make your baby sleepy or disorganized and unable to express their feeding reflexes as well.
  • Intravenous fluids given during labor can result in your baby having more fluids on board, and their weight loss may be more significant as those fluids leave their body.
  • Cesarean section birth - average weight loss is slightly higher for babies born by cesarean section than vaginal births. (6)
  • Jaundice (7) - your baby might be sleepier and hard to rouse for feeding.
  • Pacifier use - can lead to missed feeding cues. Babies who nurse for comfort as well as for food tend to gain appropriate weight compared to babies who use a pacifier regularly.
  • Premature birth - babies born prematurely have more hurdles to overcome and may gain weight more slowly in the beginning.
  • Swaddling or other sleep suits/sacks interfere with your baby's natural sleep patterns. It dampens their reactions and scrambles their intrinsic blueprint for wakefulness patterns. They encourage longer sleep, but babies are hardwired to wake during the night for food. Babies' natural habitat is in close contact with their lactating parents.

What to do if baby has lost weight

  • Be in close communication with your baby’s pediatrician and your IBCLC.
  • Hand express or pump and give the milk to your baby for more calories and to protect your milk supply.
  • Stay skin-to-skin with your baby and nurse as much as they are willing.
  • Do breast compressions during nursing.
  • Offer to feed your baby more frequently during the day, paying close attention to their cues.
  • Include lactogenic and hydrating foods in your diet to support and boost your milk supply.
  • Use high-quality lactation supplements to support milk production and encourage milk flow. Supplements are a helpful tool but do not take the place of getting to the root of your milk supply or baby’s weight gain issues.

Each baby has a unique set of circumstances to consider when looking at their overall growth. Growth charts are there to help you determine if your baby is growing well. Seeing your baby grow and thrive is very rewarding as a parent, and their growth during the first year of life is extraordinary. They will go from a newborn relying entirely on you for everything to becoming a walking, laughing, more independent, wonderful toddler. 


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