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Stupid question about dating

(22 Posts)
Sleepybeanbump Mon 29-Jun-15 13:25:11

So I know that pregnancy is normally dated from lmp. I didn't know mine and went for early scan. They dated me exactly back to the only day in that surrounding week that we had DTD so knew it was accurate.

My date got brought back 2 days at my 12 week scan (I know they're wrong, but it doesn't matter grin).

Now that's all fine, but I keep reading about these 2 extra weeks that get added on because dating is done from lmp. My dates have always tied in with conception. Why haven't the 2 weeks been added in my case? I don't want it to be, but just confused that I seem to have a different experience to what I read about.

scarednoob Mon 29-Jun-15 14:06:23

I THINK - and I may be wrong! - that LMP is used until your dating scan. after the dating scan, they stick to that date, so the LMP becomes irrelevant.

MissTwister Mon 29-Jun-15 19:42:45

This hurts my head! At the conception date you will be 2 weeks. I conceived on 5th Nov and at that point was 2 weeks. Count back 40 weeks from your due date and you should find that.

MissTwister Mon 29-Jun-15 19:43:58

To add LMP is then irrelevant ie my period was not 2 weeks before that it was only 10 days. Does that make sense?

Appleblossom82 Mon 29-Jun-15 20:21:29

I so thought this thread was going to be about dating during pregnancy!

Sleepybeanbump Mon 29-Jun-15 21:03:36

Sorry to disappoint apple!

Twister, nope, 40 weeks back from EDD takes me to conception date.

Sleepybeanbump Mon 29-Jun-15 21:08:11

Scared I think you're right- something else I read implied that. God, that must be really confusing to find that how pg you are suddenly changes by up to 2 weeks!

Also- and this is probably a REALLY stupid question, but how do they do the dating?! I mean, I know they take all different measurements at the scan, but surely it only works if all babies are almost exactly the same size, which they're not when they're born!!

Baguettes Mon 29-Jun-15 21:16:04

<was also hoping for a thread regarding dating during pregnancy grin >

Appleblossom82 Mon 29-Jun-15 21:23:56

I was going to suggest you should focus on your baby for the time being, rather than your love life. Does that help at all ? grin

MissTwister Mon 29-Jun-15 21:35:26

But it rarely would ever change by 2 weeks, its usually a couple of days. I think they're saying you conceived two weeks earlier than you think then

MissTwister Mon 29-Jun-15 21:39:31

You do want to clarify though as surely you could end up getting induced 2 weeks early?

Sleepybeanbump Mon 29-Jun-15 21:40:28

Great advice apple grin You know, with all this excess energy and blooming good health I'm enjoying, it would have been too tempting to be out there playing the field.

I think dh might have been a bit miffed too. I've already banished the poor man to the spare bedroom.

Glad you talked me out of it wink

Appleblossom82 Mon 29-Jun-15 21:42:26

Glad to be of service smile

Sleepybeanbump Mon 29-Jun-15 21:46:37

Twister I think it's ok. I've had my 12 week scan and their EDD (give or take 2 days) is the same as my EDD calculated from the date of conception (I'm certain of it as it was wedding anniversary, we were on holiday, and dh and I were mating with the frequency of giant pandas at the time grin)

The only other likely day was about 3 weeks later so was ruled out as soon as we found out at early scan that I was 7 ish weeks as opposed to the 4 we thought.

I think as scared said they do it dead accurately at 12 week rather than including the 2 week thing.

whatsoever Mon 29-Jun-15 21:46:46

I think official dating is nonsense. My official date last time meant conception was when I was still on my period & we definitely hadn't DtD yet that cycle, a week or so earlier than the date my LMP gave. DS was 10 days late. Which was in fact only about 2 days late by my reckoning. I was so hideously uncomfortable I was prepared to be induced the next day anyway though.

MissTwister Mon 29-Jun-15 22:28:14

I agree that LMP becomes irrelevant at 12 week scan but still you are calculated as 2 weeks pregnant when you conceive. So conception date = 2 weeks then its another 38 till due date. Do you see what I mean!?

MissTwister Mon 29-Jun-15 22:38:47

This is quite helpful!

Sleepybeanbump Tue 30-Jun-15 07:45:52

Oh ok, in that case I have had it added, as they've counted 40 weeks in total from conception to due date.

Is this a problem!? Does this mean I should actually be due 2 weeks before they think I am!?!?

Appleblossom82 Tue 30-Jun-15 08:04:53

Sounds like it to me sleepy. My due date is 38 weeks from when they think i conceived. The date is possible or it could be a vouple of days earlier....but doesnt make much difference. Id probably query it if i were you.

Thinking measurements would be out with such a difference though??

Sleepybeanbump Tue 30-Jun-15 08:10:17

Actually it's even more confusing than that, as this means I don't know what the conception date was, or whether they've even counted 38 or 40!

When I had my early dating scan, it dated me as 7 weeks something. Counting back took is to a week we were on holiday and we thought we knew the exact date. I assumed when they said 7 weeks they meant 7 actual weeks!

If a dating of 7 weeks actually meant 5 weeks or more (with a 2 week window for error) since actual conception, I have no idea what the exact date is. If 7 weeks DID actually mean 7 weeks since conception, then they've counted me 40 from conception to EDD which is wrong. But there's no way of telling, surely!

3 scans have all done much the same thing tho (within a few days of each other).

mummyneedinganswers Tue 30-Jun-15 08:20:57

Same happened to me so I was meant to be 7 weeks had an early scan and was only 4 weeks which mean I was actually only two that with the extra two added on it could be that u DTD one day but didn't conceive until day or two later in my cases I ovulated really late and that was why mine was different. Your two weeks are already added on x

Appleblossom82 Tue 30-Jun-15 08:23:02

If the scans are all in agreement i would go with it. But wouldn't hurt to discuss with your mw as it will have more significance later on!

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