Gestational age

In obstetrics, gestational age is a measure of the age of a pregnancy taken from the beginning of the woman's last menstrual period (LMP),^[1] or the corresponding age of the gestation as estimated by a more accurate method if available. Such methods include adding 14 days to a known duration since fertilization (as is possible in in vitro fertilization), or by obstetric ultrasonography. The popularity of using this measure of pregnancy is due to the fact that menstrual periods are usually noticed, while there is generally no convenient way to discern when fertilization or implantation occurred. Gestational age is contrasted with fertilization age which takes the date of fertilization as the start date of gestation, and pregnancy which begins with implantation.

The definition of pregnancy and the calculation of gestational are relevant in the context of the abortion debate and the beginning of human personhood.