Since there's no hard and fast rule as to when baby can go the entire night without eating, Collins takes his cue from baby: If baby is gaining weight appropriately in the first weeks of life, Collins might give the go-ahead for allowing baby to sleep as long as he wants at night. "If baby comes in at a week or two and is losing weight or has just gained a couple of ounces, I'm more direct about how frequently to feed the baby." Most experts don't recommend forcing baby to sleep through the night — in others words, not feeding him should he wake up — until baby is at least 4 months of age.
Babies' habits will vary widely by baby, but roughly 25 percent of babies will sleep through the night by 2 months, 50 percent will do so by 4 months and 75 percent will sleep through the night by 6 months, says Collins. "It just depends on when baby is ready. A baby can be 18 pounds and still waking up," he adds.
Helpful hint: Once baby has sipped from a bottle, it's not a good idea to reuse the milk or formula in the bottle, even if baby hasn't eaten much. The reason: baby's sucking introduces bacteria into the milk.
During the first four months of life, Unger and Collins recommend an entirely liquid diet — of either breast milk or formula. That means you shouldn't heed well-meaning friends' advice and slip baby cereal in his bottle in the hopes that he'll sleep longer. Baby isn't ready for cereal and, besides, there's no evidence that cereal actually helps keep baby's stomach full longer. "We want to go at baby's pace," says Collins. "He'll be ready for cereal when he can open his mouth, accept a spoon and be part of the meal," he says.
One exception to the milk-only rule: Breastfed babies can benefit from a vitamin supplement. "There is some new information that suggests that babies who are purely breastfed should also be on a vitamin D supplement," says Unger. "It's based on the fact that with the increased use of sunscreen babies are not getting as much vitamin D naturally." Your pediatrician can suggest an over-the-counter vitamin supplement.
