1) 38 weeks is "full term" because MOST babies can survive just fine at that point (remember, *most*, not all). When mom has a medical condition, 38 weeks is the holy grail - if she can get that far, they can bring out baby knowing it will more than likely be okay.
2) EDD's are based on the assumption that every woman has a 28 day cycle and ovulates on day 14. Since these are only averages of women's cycles, it's quite possible for a EDD to be off by two weeks or more on either side of the date you get at the doctor's office.
3) Babies come when babies are ready. Some are ready in 36 weeks (I know a lady who consistently has babies between 36 and 37 weeks who are "fully cooked"). Other babies aren't ready until past the 42 week mark.
4) 40 weeks represents the median (average) of the month in which most women will give birth. Average means some will go earlier, some later.
at 6:21 PM on Sep. 25, 2009