How Much Weight Should My Baby Gain?

by Dr. Pamela Bandelaria, pediatrician

One of the most exciting things about being a parent is watching your baby grow.  However, it's sometimes difficult to know how fast your baby should grow or whether they are putting on the right amount of weight for their age.   This article will outline the average weight of your baby at birth, how much weight your baby should gain every week until they are a few months old, what affects their weight gain, and when you should be worried about your baby’s weight gain.

What is the average weight of a baby at birth?

At birth, a baby typically weighs between 2.5kg (5.5lb) to 4.5kg (10lb). Babies born at less than 2.5kg are classified as low birth weight babies, and this often occurs when babies are born prematurely.  These babies are at a higher risk of developing diseases and complications. However, not all low birth weight babies have problems.

Regardless of the birth weight, your baby will follow a pattern of growth that involves a fluctuation of the weight before a steady increase. Many babies lose 10-12% of their birth weight during the first week of life, termed physiologic weight loss. It occurs because of the adjustment of nutritional intake and the elimination of excess fluid in the baby's body after birth. A baby's nutritional intake changes after birth because aside from them adapting to breastfeeding, sucking, and latching, the breast milk during the first week of life is composed of colostrum (containing antibodies) and less fat, which causes the baby to lose weight.  As breast milk matures, it develops a higher fat content, and with your baby's ability to latch and suck better, their birth weight catches up.  By the second week of life, most babies will have gained the weight they lost after birth, if not more.

How much weight should a baby gain in the first month?

After the period of physiologic weight loss where excess fluid is lost, your baby catches up to their birth weight and continues to grow. Within the first month of life, your baby would have gained approximately 30g (1oz) of weight per day.  This is the fastest growth period of your baby's life.   Their body is adjusting and changing to give them the strength and capacity to explore the world around them as they continue to develop.

How much weight does a baby gain in the first few months of life?

During the third month of life, the growth rate of your baby is expected to slow down. From a gain of approximately 30g in the first month, your baby will only gain about 20g/day in the third month. During this period, your baby explores their surroundings and learns to roll over and reach out for objects. Body growth is not the priority at this time, as most of their energy is expended in exploration.

By the fourth month of life, your baby will have grown so much that their weight is double their birth weight.   By their first birthday, their weight will have tripled, and by the second year, they would have quadrupled their birth weight.  However, this is just a rough estimate of the average weight gained by most babies. It doesn't mean that if your baby does not hit this mark, that there is something wrong with them. There is always an allowance and a window for your baby to catch up with their growth.

How much weight should a breastfed baby gain each week?

As mentioned above, a baby will gain 30g per day (approximately 210g per week) until they reach the three-month mark, after which it slows to 20g per day (around 140g per week). Since exclusive breastfeeding for the first six months of life is recommended by the American Academy of Pediatrics, this growth pattern applies to all breastfed babies. It is also the same growth trajectory for formula-fed babies and those fed both breast milk and formula. These values are just average values and may vary.

Do breastfed babies gain weight slower?

There is are various theories as to whether breastfed babies gain weight slower or faster. In some cases, breastfed babies gain weight faster, attributed to the caloric content of breast milk.  However, some breastfed babies gain weight slower because of the barriers to breastfeeding.   These may include the mother not producing enough milk or the baby having trouble with latching and suckling. Because breastfeeding and breast milk vary from mother to mother, it is hard to say how breastfeeding affects babies' weight gain, and studies on whether breastfed babies gain weight faster or slower have mixed results.

How do I know if my baby is gaining enough weight?

The estimated gains of a baby daily and weekly previously mentioned are simply an estimate to gauge whether your baby is gaining enough weight. At around these milestones, healthcare providers check your baby's weight so that if it is markedly different from the expected weight gain for that age, other diagnostic tests can be performed to determine if your baby is healthy.

Aside from weighing your baby regularly, you will know if your baby is gaining enough weight by the amount of milk they are getting.  If your baby is drinking expressed milk, it can be easier to quantify than when your baby is feeding directly from the breast. However, if you know your baby is latching and feeding correctly, she will likely be receiving enough nutrition. 

There are other ways to estimate if your baby is gaining enough weight. For example, another way to assess if your baby is getting enough milk, and therefore gaining weight, is by measuring your baby's output through checking stool and wet diapers. By looking at the number of wet diapers, we can estimate your baby's urine output, and checking how many times they pass a stool per day will determine whether they are feeding enough.  Usually, a healthy baby will poop after every feeding, and diapers will have to be changed frequently, but this varies significantly from baby to baby. 

When should I be worried about my baby's weight gain?

Your baby's weight gain can be tracked during well-baby visits or when a doctor sees you for routine vaccination. There are standardized growth charts on which your baby's weight can be plotted to see if they are within the correct weight range for their age. You can also keep track of your baby's weight at home if you have the proper equipment.

As mentioned previously, all babies are different, and some grow faster, and others grow slower.  It is normal for your baby to lose weight or encounter a plateau in their weight gain. However, these moments should only be brief, and if your baby is within the acceptable measurements when plotted on a growth chart, there is usually no cause for concern.  In general, even if the weight gain is slow, it should be steady. You or your doctor should only be concerned about your baby's weight if there is no growth over an extended period.  If your baby plateaus in their growth for an extended period, or if there is a noticeable decrease in weight from the previous check-up, it is best to have them assessed to see if there are any other problems. Likewise, if your baby falls below the expected weight, it is also best to have them checked.

There can be many reasons why a baby would not gain weight at a rate expected for their age. However, the most distressing reason for poor weight gain would be dehydration. Dehydration may seem like a trivial illness for adults, but for children and most especially infants, it can be dangerous and sometimes even life-threatening if not treated early. Since the body is made up of water, and body water contributes to the overall weight, severe dehydration can affect the weight. Therefore, babies who are not gaining weight should always be checked for dehydration. Signs of dehydration include a sunken fontanel, sunken eyeballs, dry lips, drowsiness, weakness, or the appearance of dark circles under the eye. You can also note that your baby may be dehydrated if they produce fewer dirty and wet diapers than usual. If you notice any of these symptoms in your baby, do not hesitate to go to your nearest physician.

Conclusion

Weight is one of the ways to check if your baby is developing and growing as they should. A baby who has continuous weight gain is healthy. In general, a baby's growth pattern is as follows: a baby will be gaining 30g/day until the first few months of life, which will then decrease to 20g/day afterward. Your baby's weight usually doubles the birth weight at four months, triples at one year old, and quadruples at two years old. It is also normal for your baby to lose some weight during the first two weeks of their life, termed the physiologic weight loss, which they usually regain after the second week of life. Having your baby checked if you have concerns about your baby's weight will help identify other problems which can account for poor or slow weight gain.