How Common is Prematurity Frequently Asked Questions Introduction Prematurely born babies differ a lot depending on how premature they are. Some are only slightly premature and go home with their parents after a short hospital stay. Others are extremely premature, and stay in the hospital for many months. To know the kinds of problems you are likely to face with your prematurely born infant, you need to know how premature your baby is. The duration of a pregnancy is measured by gestational age.
Gestational age is basically a measure of the length of time that a baby spends in the womb.
It is generally calculated as the time from the first day of the last menstrual period to the day of birth. Conception occurs on about day 14 after the first day of the last menstrual period. However, this date is not usually known. The first day of the last menstrual period usually is known. Therefore the beginning date for the pregnancy is the first day of the last menstrual period.