Gestational age is the age of an unborn baby measured in weeks and days, not in months. Since the exact day the baby's conception is typically not known, the gestational age is based on the date of
the your last menstrual period. Forty weeks after the first day of the last menstrual period is the estimated due date. But it is important to remember that this is still just an estimate and
less that 5-10% of babies are born on their estimated due date.
As mentioned above, the gestational age is calculated from the
first day of your last period. An early exam of your uterus can also help in the estimate of the baby's gestational age. The most accurate way to determine gestational age is a reliable date of
your last menstrual period confirmed by an ultrasound exam. Your health care provider will discuss an ultrasound with you.
The progress of a pregnancy can be judged as normal or abnormal only when the gestational age is known. Gestational age is also very important if any complications occur, if early delivery needs to be considered, or if the baby
needs to be monitored because the baby is overdue.
To help you estimate your own due date, use this pregnancy calendar. Remember that it is best to start prenatal care with your midwife or doctor as soon as possible.