A premature or preterm birth occurs when a child is born at or before 37 weeks gestation (most pregnancy last about 40 weeks). According to the march of Dimes, about 12.8 percent of babies born in the US each year1 in 8 birthsare premature.
Irregular menstrual periods or first trimester vaginal bleeding can confuse gestational age estimates. To improve the accuracy of gestational age estimates, many doctors use an ultrasound examination before about 20 weeks gestation to help confirm or correct the gestational age estimate.
Another way to estimate prematurity is the baby's birth weight. In general, the more premature infants are, the less they will weigh.
There are several terms used for this:
- Low-birth-weight (LBW) indicates that a baby weighs less than 2,500 grams (about 5 lbs., 8 oz.) at birth
- Very-low-birth weight (VLBW) indicates that a baby weighs less than 1,500 grams (about 3 lbs., 3 oz.)