Dating a pregnancy

[bettybat]

Have been really curious about this, because it doesn't make sense to me!

I know the 48 hour window of conception - I was doing ovulation tests to check I was ovulating, it was the very beginning of our TTC and I was just beginning to observe my cycle and make note of it etc. I got positive tests on days 13 and 14 - and we DTD both days and had done up all that week anyway so no idea about the gender determining thing, and we were lucky enough to get pregnant that month. My cycles were between 27 and 31 days long. I dated what would have been my next pregnancy at an average of 30 days just to be sure.

So my question - the doctors and nurses took my date from the first day of my last period, standard yes? But I know it can't possibly be...aged from that date because I know conception was 13 or 14 days from the date they are working off - or 9 or 10 if you work from period end.

Had my scan last week and working from their aging, I was 12+3 - but working from conception, really 10+something. From the size of my little wriggler, they re-dated me at 13+4 - taking me even further away from it's actual age!

So now I'm thinking - when it comes to them saying I am overdue, if it comes to that, will I actually be? Or will wriggler just be hanging around a couple more weeks as it would if everyone dated from conception? It's important to me not to be induced if possible and it just makes me wonder - surely doctors and midwives know conception doesn't happen on the first day of your last period So why do they do it like that?

Years ago your average woman didn't have access to all the tools we ourselves have now to track fertility - and inadvertently or deliberately - know ovulation times. But we do now - so why don't they take that into account? I know individual gestation weeks can vary but still...

I'm guessing there's a reason if they insist on keeping that way of dating things but I can't see why...curious minds wish to know!

Sorry I won't be very helpful most likely but as far as I know pregnancy is always dated around 2 weeks before conception? Although get where your coming from with the re-dating.
I would say maybe towards the end don't get induced if you're 'overdue' for a couple of weeks
Anyway someone who knows what they are talking about should be along soon.

im not sure anyone will have the exact answer for you as you are asking why something is done that has always been done that way, pg is always dated from the first day of your last period, with your scan putting you further ahead than that may have something to do with your cycles being slightly shorter sometimes, mine are longer 35 days so i was a week later than they originally dated me. in terms of ovulation not all ladies know exactly i certainly didn't as wasn't using opk sticks, and when the egg gets fertilized can make a difference, so there is always a chance you ovulated early/late and it didnt fertilize straight away

you can refuse to be induced and they can monitor you, and you obviously don't have anything done until around 42 weeks, I've never had that problem though as mine come early!! lol i personally wouldnt want to go over to much as I've had experience of a friend loading their baby due to being left too long as the placenta wasn't as effective???
congratulations on your pregnancy im sure after a few months you'll be willing the end to be near lol :)

losing their baby!!! bloody phone :)

I may be wrong here (and I'm sure I am having not had any children!), but I thought actual pregnancy is usually about 38 weeks, but they say 40 weeks to the "due date" and this allows for the extra two weeks (on average) from the date of your last period..??

Am I just being thick?

That's my understanding too retired.

And I am pregnant and did the whole thing. Then came to that conclusion. So when they say you're 12 weeks, it doesn't mean the embryo is 12 weeks old. It means you're 12 weeks pregnant, which means something slightly different.

Yup I had to ask this question too!

They date it from first day of last period. Therefore I am said to be 6 weeks pg, as it's 6 weeks from last period, even though it is only 4 weeks since I ovulated and therefore since I could possibly have conceived.

They add an extra 2 weeks to the gestation period (40 instead of 38 weeks) to cover this.

The reason they date it from last period is because many women don't know when they ovulated (or could be wrong).

So I am 6 weeks' pg but embryo is 4 weeks gestation.

Just dropped by this thread as looked Interesting as i too thought i cant be 6 weeks as ov on / around 2 weeks later! Looks like I'm 6 weeks ( but actually 4) like you minipie
Whats your edd?

mytime it's 8 December, I think I'm actually about 6 weeks 5 days so nearly 7 weeks (god it's going slowly! damn those early pg tests )

It does doesnt it. I just want to get to 3 month quickly for peace of mind etc.
According to my dr Im due 16th dec so not far off u

My dating scan was wrong with my daughter I knew the dates of my lmp and the date I conceived my due date should of been 16 April but they gave me 22 a full week out. Didnt affect me tho as I gave birth on 16.4.08 when I was supposed to. However I would not worry too much about the date given because you will be 41&5 before they will induce you making you full term anyway. my friend was given a due date and then at 16 week was given a different one so if it is a big deal they can look into it for you. Hope this helps

It can be a problem, though.

In my case, the dating scan measurements and EDD meant I would have conceived on CD4 - which is highly unlikely given that I had barely finished menstruating and DH and I hadn't actually done the deed since before my period began. As we were TTC, I was watching my cycles very carefully, including physical signs that I was ovulating - from these observations, I reckon I ovulated on CD12 or 13. The EDD I was given was a good week earlier than by my own calculations/that of my lmp.

Thing is, because I am over 40, I've been told I would be given an ELCS on my due date if the baby hasn't arrived naturally by then (I'm hoping for a VBAC). They don't give you as much leeway to be overdue because some studies suggest a greater risk of stillbirth in over-40s who go overdue (the consultant was at pains to stress that there is no agreement on whether this risk is actually higher or not - but it might be).
But I believe I won't actually be overdue until more than a week later, so it gives me less time to avoid another CS (they almost certainly wouldn't induce because of the previous CS).
I can refuse the date they give me and opt for a later one if I accept the (possibly hypothetical) risks involved and I probably will do that. The issue has caused me a bit of consternation, though.

Might all be academic, of course. DD arrived four weeks earlier and who's to say there may be some other reason to have a CS (DD was delivered that way because she was breech)?!

And yes, average human gestation is 38 weeks, but they add on an extra two weeks to date the pregnancy from the lmp date - because most women ovulate on or around CD14 - so in medical terms, you're always two weeks more pregnant than you actually are.

It's bonkers and complicated, taking weeks away here and adding them there...it's not like they don't know about ovulation versus periods

Glad to see I'm not the only one confused though!

Best advice I could give is tell your midwife and ask for second oppinion thays what I would do or ask her to explain more clearly she is trained in that weird dating thing

Just go with what the dating scan says. Mind you the scan is not always accurate. I am pregnant thru IVF with ICSI so I know to the hour when conception occurred, yet I still had my due date moved forward a day! My friend also ivf had hers moved back 2 days. The only time it is likely to matter is the induction dates, and it would be your right to refuse an induction if you felt strongly against it. Most people don't know when they ovulated, so dating from last period is a best guess for most people i suppose.