A premature infant is a baby who has spent less than 37 weeks in the womb. The average length of pregnancy is 40 weeks. So a premature infant is one who is born 3 weeks or more before the due date.

What is going on in the body?

Premature babies have not developed completely. The earlier a baby is born, the less developed its organs are. Premature babies tend to have very specific problems related to their underdeveloped organs. Sometimes the treatments that they receive for their underdeveloped organs also can lead to problems. For example, a baby born after only 24 weeks in the womb doesn't have fully developed lungs. Because of this it cannot breathe well on its own. It will probably need the help of an artificial breathing machine, or ventilator.

What are the causes and risks of the condition?

Certain factors in the mother are linked with the birth of a low-birth-weight infant. These factors include the following:

Some babies have factors themselves that make them more likely to be born early. These factors include being one of multiple babies in the same womb, such as twins or triplets. The baby may have physical problems or a bloodstream damaged by infection.

Sometimes there are problems with a mother's womb. The placenta may not be adequate to support the baby to full term. The placenta may be in an unusual location, such as placenta previa. When the mother has a chronic illness like diabetes, congestive heart failure, or high blood pressure, she is more likely to deliver early. Certain infections in the mother, such as genital herpes or syphilis, can cause the baby to be born early.