Most babies are born about 40 weeks after the first day of their mother's last menstrual period. But about 10 percent of babies arrive sooner. Any baby born more than 3 weeks before its due date is considered premature.
Premature babies have less time to fully develop and build strength in the womb.
As a result they're often at increased risk for medical and developmental problems. One of the biggest problems facing premature infants is underdeveloped lungs. If your baby is born early and has trouble breathing, he or she may need help from a ventilator. Even a few extra days can give your baby's lungs a chance to become more mature. But sometimes, in spite of every effort, your baby may be born early.