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How much weight should a breastfed baby gain each month?

mother breastfeeding her baby


On average, how much weight should a nine-month old breastfed baby be gaining per month? I know that weight gain may not be as rapid as with a formula-fed baby and that the guidelines and percentiles charts used today were compiled from data on mostly formula-fed babies. My nine month-old girl has only gained nine ounces in six weeks and on the percentile charts sits below 10 percent for age to weight, and my friends’ formula fed babies are now almost 10 pounds heavier at the same age. I keep telling myself that it’s because of the formula and that they are actually overweight babies. My paediatrician seems happy with her health but when she sits next to those giant babies it’s hard not to worry.


To answer your question, I consulted Dr. Jack Newman.

The most important issue is whether your baby is drinking well at the breast. Sometimes babies who were doing very well and gaining weight with exclusive breast feeding start to gain weight more slowly after three or four months compared to formula-fed babies and this indeed is considered normal. As Dr. Newman points out and you suggest, the more rapid weight gain of the formula fed baby is not necessarily the standard.

Sometimes the addition of cereal to a baby’s diet may change the pattern of weight gain. It might be that the baby is being given a restricted quantity (as often the doctor might say give two tablespoons) as opposed to allowing the baby to eat as much as the baby will eat without pushing food. Some babies refuse food if the parents are feeding them and you might allow the baby to feed herself with her fingers.

If you are exclusively breast feeding, it is indeed possible that your milk production has decreased. Possible reasons for decreased milk supply include:

  • going on the birth control pill or having had an IUD inserted that has a hormone associated with it
  • pregnancy
  • stretching out the feedings as a way of training a baby to sleep through the night
  • bottle feeding, which might cause the baby to latch on to the breast less well and get less breast milk or not empty the breast
  • emotional upset
  • illness and some medications

Sometimes the milk supply decreases for no obvious reason. Finally, the possibility of illness in the baby should not be dismissed.

I think you should be reassured that your doctor is pleased with your baby’s health and while it is hard, as you say, not to worry (that is what we often do as parents!) I do believe you are right that often the formula fed baby is overweight. Nevertheless, I would encourage you to speak with your doctor to voice your concerns and have them addressed.

Published May 2010

a man carrying two children

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