Determination of which time point is to be used as the origin for gestational age. This starting point is the woman 's last normal menstrual period (LMP) or the corresponding time 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.
when do many obstetricians date the onset of pregnancy from
the woman 's last normal menstrual period (LMP)