OK, this won't apply to everyone (like Periwinkle, who delivered early or Amy, who is pg for the first time), but the midwife I interviewed the other day said that with your 2nd, you can often go by how long your last one took to "cook", so to speak (assuming you know/remember your dates). My 1st took 256 days from ovulation to birth. So I just counted 256 days from ovulation (May 20) to wind up with Feb 1 as an edd. But since I don't really put much faith in edds I'm just saying "around the 1st week of Feb". Of course it's nice for us as the expectant mamas to have a date to dream about, but when certain medical professionals get a hold of a "due date", it can sometimes wreak havoc. I know a woman who ovulates on day 28 of a 32 day cycle. If her OB uses the typical calculation from the LMP, her edd could be off by two weeks or more, which could lead to an induction...
I also don't think it's reasonable to think that women with different cycle lengths, metabolic rates, diets, exercise regimens, ages, temperaments, levels of stress etc are all going to produce a baby in the same number of weeks. But *in my limited experience*, OBs, nurses, even some CNMs don't believe you when you tell them what day you ovulated; they prefer to rely on their ridiculous little charts that only use the LMP to come up with your edd, by which your pregnancy may be tyrannically governed (when I think about it, I'm amazed they even trust us to get that much right
). Basically, they don't really think that you know more about your body than they do. As my one pregnant friend was told when she called her clinic to make her first prenatal appoint ment, "Honey, you're not pregnant until we say you are."