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Working out EDD

(8 Posts)
NerdyBird Tue 15-Apr-14 15:32:28

As far as I know, LMP is used because women are more likely to remember when their last period was than be able to tell when they ovulated. My LMP can't be used as I had a random double-length cycle when I conceived so it would make me 4 weeks more pregnant than I am.

Raxacoricofallapatorius Tue 15-Apr-14 11:11:45

They use your LMP and cycle length as a guide. For example, I know I ov on day ten and have short cycles and my mw adjusted accordingly. They use this to plan the dating scan and then use the date from the scan once it is performed.

But I think the op is just confused as to why you are dated as two weeks pg at the point of conception and it's just that historically, they dated a pregnancy from LMP which in the average woman is two weeks before conception.

Teatimecakes Tue 15-Apr-14 11:06:28

You work it out from the first day of your last period, not from dtd day

ithinkineedahug Tue 15-Apr-14 11:06:26

Thanks for clarifying!

HolidayCriminal Tue 15-Apr-14 11:05:56

Is it not still dated 40 weeks from last Menstrual period regardless of women's usual cycle length? I know they were very inflexible about that for dc (am now getting on a bit, though).

"They" will (ime) take the scan date estimate over all over data, though, which is accurate to within 3 days as long as it's scanned in the 11-13.5 week window.

Raxacoricofallapatorius Tue 15-Apr-14 10:48:03

In an average woman this is 40 weeks from your last menstrual period.

Raxacoricofallapatorius Tue 15-Apr-14 10:46:51

Pregnancy is dated from 2 weeks before actual conception.

ithinkineedahug Tue 15-Apr-14 10:45:15

I'm very confused and hoping someone can help! I had cd1 on 28th March. Ovulated on 11th April...dtd so had a play around with an online calculator just to see if I did get a BFP when the EDD would be...and it reckons based on the info I would be 2 weeks 4 days....how? when we only dtd at the weekend and hadn't for at least a month or so before using contraception?

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