If your baby isn't getting enough to eat overall from breastfeeding, you have to figure out and then fix the problem. As with everything in life, it's easier to fix a problem when you know what's causing it.
There are various reasons why some babies have trouble getting a full feeding, but a lot of it stems from a newborn's stamina, or lack of it. Babies need a steady milk flow to keep sucking, and if that flow slows down, your baby will slow down too and might even stop feeding.
Sleepy baby: Newborns sleep a lot. And since nursing lulls them, they often fall asleep before they get enough to eat, then 20 minutes later wake up and start rooting again. Your goal is to try to keep your baby feeding effectively for as long as possible at each session. Keep in mind that your best efforts—breast compression, switch nursing, putting your baby down on the floor—might not be 100% effective until she has had some time to grow out of this sleepy phase.
You should also know that premature and jaundiced babies have low stamina when it comes to feeding. You need to be extra careful they don't sleep through feedings.
Edema: Also known as fluid retention, edema can affect your milk flow or supply. Women with postpartum edema, which causes swollen feet, ankles and lower legs, often have trouble with their milk flow until the condition goes away.
Engorgement: Sometimes when the milk comes in, the breasts are so engorged the milk may have trouble flowing freely. After a good drainage and the engorgement goes down some, this problem usually resolves itself.
Slower rate of milk flow: This is the most common problem. Many women have a slower rate of milk flow as their milk is coming in. In fact, some never experience engorgement or the sense of their milk coming in at all. Instead, it's a slower pace to a full milk supply and therefore a slower rate of flow.
When this happens, your baby might have trouble accessing a full feeding and could slow down or stop nursing right when you need her to keep going to fully drain your breasts and help increase your supply.
While the notion of supply and demand is true in the basic sense—the more your baby demands, the more you supply—if breastfeeding isn't going well, this theory flies out the window. If your baby falls asleep or shuts down when your milk flow drops, she's "demanding" very little, even though she's still on your breast. But being on your breast doesn't mean she's draining it.
Sometimes you'll never figure out why your baby isn't getting enough from your breasts. It could be a combination of a few of the factors mentioned above. The main thing is to try to fix whatever you think is causing the problem. Most of the time, the issue is easily resolved by adjusting your milk supply and flow.
Source: Heather Kelly is an International Board Certified Lactation Consultant (IBCLC)