Gestational age is the age of an unborn baby.
It is measured in weeks and days, not in months. Since the precise date of conception is seldom known, the age is based on the date of the mother's last menstrual period. Forty weeks after the first day of the last menstrual period is the estimated end of a normal term pregnancy, or due date. The progress of a pregnancy can be judged as normal or abnormal only when the gestational age is accurately known. Gestational age is very important when complications occur in the pregnancy and early delivery may be necessary.