Expert answer: Lane France, pediatrician
Ideally, your baby should be at least 2 to 3 months old before you take him or her on an airplane. This will give your baby's immune system a chance to grow strong enough to resist the germs that often make the rounds in airplane ventilation systems. It also gives the two of you enough time to settle into a routine and master the art of breast- or bottle-feeding.
If you can't wait that long, your baby should be okay to fly after his or her 2-week checkup – provided there is a clean bill of health and you had a full-term pregnancy without complications. Premature babies are especially susceptible to germs, so it may take longer before they're ready to go on an airplane trip.
If you have any questions about whether your baby is healthy enough to fly, ask your doctor for advice. Note that airlines do not allow any baby younger than 1 week old to fly without a doctor's note.
Many parents worry that the changes in air pressure that happen when you fly can harm their baby's ears. It's true that "popping ears" during takeoff and landing can be a bit painful for infants, but it won't cause any lasting damage. (The pressure changes can be very uncomfortable if your baby has an ear infection, however. If so, you may need to postpone your flight.)
Your baby will feel more comfortable with something to suck on during takeoff and landing, so you may want to breastfeed or give a bottle or pacifier. You can give your baby some infant pain reliever (such as acetaminophen) if his or her ears really seem to hurt.