The average pregnancy lasts about 9 months, or 40 weeks. But for one in eight moms-to-be, the baby is born at least 3 weeks before the due date. That’s called a premature, or preterm, birth.

Because the infant has less time to develop in the womb, premature babies are at greater risk for medical and developmental problems. In fact, premature birth is the leading cause of death among newborns; dangerous conditions, such as bleeding in the brain and breathing trouble, can occur. Some infants may require special care in a neonatal intensive care unit. Because of immature skin, poorly developed temperature control by the autonomic nervous system, and a lack of body fat, they are kept in an incubator—an enclosed plastic bassinet—to regulate their body temperature.

In about 40 percent of premature births, the cause is unknown. But scientists have identified some causes: Preterm births can be brought on by bacterial infection within the womb and inflammation in the mother, whether it’s caused by a sexually transmitted disease or systemic infection. Physical or mental stress possibly is another factor, because stress hormones can stimulate the release of other hormones that trigger uterine contractions and premature delivery. An incompetent cervix; rupture of the amniotic sac; preeclampsia (serious complications occurring late in pregnancy); injuries or diseases that cause uterine bleeding; and the overstretching of the uterus due to anatomical abnormality, excessive amniotic fluid, or a multiple pregnancy can also lead to contractions.

If a mother begins preterm labor, physicians will try to keep the fetus in the womb so it has more time to develop and so that steroids can be administered to mature its lungs. For instance, women who aren’t undergoing contractions but have a widening cervix may undergo a cervical cerclage. During this surgical procedure, the cervix is stitched closed with sutures. For those undergoing contractions, medications that stop or slow them may be administered. After birth, a baby is released from the hospital when he or she can breathe without support, maintain a stable body temperature, breast- or bottle-feed, and gain weight steadily.

ADDITIONAL FACTS

  1. One of the smallest babies to live, Rumaisa Rahman, was born 14 weeks early in 2004. She weighed 8.6 ounces, or a little more than half a pound.
  2. The number of premature births in the United States has increased 36 percent over the past 3 years.