For Patients/Families

Premature baby
A baby born three or more weeks before the due date. The duration of a pregnancy is measured by gestational age. Gestational age equals the amount of time elapsed since the first day of the last menstrual period. A normal gestation lasts 40 weeks or 279 days. If delivery occurs before 37 weeks gestation, the baby is considered prematurely born. About 11% of all babies are born prematurely by this definition.

Irregular menstrual periods or first trimester vaginal bleeding can confuse gestational age estimates. To improve the accuracy of gestational age estimates, some doctors use an ultrasound examination before about 20 weeks gestation. Ultrasound findings help your doctor to confirm or correct the gestational age estimate.

Birth weight can also indicate whether a baby is born prematurely. Babies born with a weight of less than 2500 grams (about 5 ½ pounds) are considered low-birth-weight babies. Generally, infants with a birth weight less than 2500 grams are premature. However, babies can be premature but weigh more than 2500 grams at birth. They can also be born at term and weigh less than 2500 grams. There is no perfect system for categorizing infants and both measurements, birth weight and gestational age, are used.

Many premature deliveries occur close to term (see below) and these infants generally do well. Infants born more prematurely than 32 weeks gestation routinely require lengthy stays in a Special Care Nursery. These infants are also at risk for long-term problems. The risk of complications accelerates as gestational age decreases. Children born 16 weeks prematurely have many-fold more complications than those born 8 weeks prematurely.