That is correct, which is why I said “round about the middle of the menstrual cycle” and not “round about the middle of menstruation”.
To clarify:
Pregnancy is dated from the beginning of the last menstrual period (LMP).
Conception occurs at the time of ovulation, about two weeks after the LMP (though this varies by a few days either side according to the length of the individual’s cycle).
This is simply a convention used in dating pregnancies, not an assertion that the foetus actually existed two weeks before it was conceived.
To return to the note on the website:
This is unambiguously true.
There are two possibilities here:
the note is trying, albeit rather clumsily, to explain how the beginning of a preganncy is dated; or
the note is asserting that a foetus has already existed for two weeks at the moment of conception.
On all the evidence, in particular the foregoing sentence and the context of the note (a week-by-week guide description of a pregnancy) I think the former construction is the only reasonable one. (Though I would be interested to hear any compelling arguments for prefering the latter interpretation.)
I assumed that jab1’s rather huffy response to it was a result of him not knowing how pregnancies were dated.
As I said in my previous post, any book or website on the subject will verify this.
Depends on the context. All the charts that tell you whether your baby has developed earlobes yet and how much weight you should be gaining are dated from the date of the last menstrual cycle, and assume that pregnancy lasts for 40 weeks.
On the other hand (and this is a little more germane to the OP), if you’re going in to get an abortion, they often tell you that they want to do it within 8 or 10 weeks of conception, and they’re generally counting conception from when it actually occurs.
When you go to the OB/GYN for a pregnancy test, they ask you when the first day of your last period was and use this and their little Mystic Wheel to determine a tentative due date which may be changed after an ultrasound.
Another ultrasound is performed at the clinic when one goes in for an abortion to verify how far along the patient is, based on the size and development of the fetus.
Dating from the day of conception would require knowing the day of conception and if you’re having sex more than once a month it’s not always possible to determine which was The Day. Women only get one period a month, though, so it’s easier just to pick that day and settle on it, even if it ends up being a couple weeks off in actuality.
When I read the OP, all I could think of was Twins!?! Now I am really scared!
I just couldn’t get over the coincidences.
And now I just can’t help thinking that the end is really here.
I don’t really have anything to add here, except to say to Fenris that your parody is the funniest thing I’ve ever read here! And saying something, as there’s a ton of hilarious stuff on Straight Dope. I nearly broke a rib laughing
