The signs that your baby is getting enough nourishment overall from breastfeeding are simple, but it's still important to monitor them in the first days and weeks. They are: diapers, weight gain, and infant behavior.
In many cases, you'll be able to see your baby plumping up every day. As the weeks go by, her face will fill out and her arms, legs and torso will become rounder. Her newborn clothes may start to fit more snugly, as will her diaper.
All of these important signs will help boost your confidence in breastfeeding. But it's also a good idea to monitor the numbers on the scale rather than obsess about them. When it comes to weight gain, there are two rules of thumb:
The pattern of your baby's weight gain is often more telling than the actual number. Here are two scenarios where both babies are gaining weight, but the pattern of one indicates there might be a problem:
Birth weight Day 3 weight Day 7 weight Day 14 weight
Baby A 8 lbs, 3 oz 7 lbs, 9 oz 8 lbs, 1 oz 8 lbs, 10 oz
Baby B 7 lbs, 5 oz 7 lbs, 2 oz 7 lbs, 5 oz 7 lbs, 7 oz
Baby A is doing fine and meets both parameters: She's back to her birth weight by Day 10 to 14 and gaining between half an ounce and an ounce each day.
Baby B looks fine from his numbers, but if you look at the pattern, you'll see he's gaining weight slowly. Why? Because if you notice his Day 3 weight, you'll realize he didn't drop much weight after birth, so getting back to his birth weight isn't much in terms of gain. And between Days 7 and 14 he only gained 2 ounces, which is below average. This could mean that he isn't nursing well.
Again, don't obsess over the numbers but keep an eye on them and look at the big picture—the pattern of weight gain. As long as your baby's weight is following the two rules, everything should be fine.
Source: Heather Kelly is an International Board Certified Lactation Consultant (IBCLC)