A normal gestation lasts 40 weeks or 280 days. If delivery occurs before 37 weeks gestation, the baby is considered prematurely born. 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 is lower when a baby is born prematurely.
They can also be born at term and weigh less than 2500 grams. Many premature deliveries occur close to term and these infants generally do well. For example, only 1.9 percent of all infants born in 1997 were born at less than 32 weeks gestation. These infants routinely require lengthy stays in a special care nursery. These infants are also at risk for long-term problems.