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Doctor gave a deliberately inaccurate due date - why?

(47 Posts)
Fenaklu Fri 03-May-13 13:26:21

I found out a couple of days ago that I was quite pregnant (more than 3 weeks on digital test). Last period was 7-9th March but due to illness on holiday, 14 hour flights and jetlag etc, the earliest possible conception date was 18th March.
My GP has just given me a due date of 11th December which makes me 8 weeks pregnant when I am only 6 and a half weeks (from known earliest conception date). This makes my real due date 10 days closer to Christmas - something we really needed to know!
Why the deliberately innacurate calculation???
(This is my first at 41, so he has no previous gestation data to go on)

Featherbag Sun 05-May-13 09:45:38

Hi, welcome to the club! Have you introduced yourself in the December ante-natal thread yet? I'm due 7th December (based on LMP), but this is DC2 for me so I know that a) this will change with every scan and b) baby will turn up when it bloody well wants to anyway (at 32 weeks in my case!).

Celaun Sun 05-May-13 09:40:11

That's the way pregnancies are dated - 40weeks from last period. It means it actually always includes approx 2 weeks when you wen't actually pregnant but that is the case for everyone. You will also get an estimated due date at your 12 week dating scan based on fetal measurements.

Quilty Sun 05-May-13 09:30:35

Even if you know the exact date of conception, dates are still calculated from an estimated LMP. Even for IVF couples, the date is still calculated as though it was a natural conception so that the measurements from the dating, anomaly and growth scans fit in with the charts. If we didn't do this then measurements would appear to be underestimated by around 2 weeks.

As others have said I find it quite bizarre that you would think the doctor had purposely given you the wrong dates! I think you need to try and not be so suspicious and trust that the people involved in your care actually know what they're doing!

Bodicea Sat 04-May-13 23:26:28

In most hospitals they take LMP date over date from scan unless there is more than 7 days difference or pt doesn't know LMP date. I am a sonographer and it annoys the hell out of me that I go to the trouble of getting accurate measurement to give accurate date and then they ( that is that powers that be) choose to ignore it!! angry

Booboostoo Sat 04-May-13 23:04:32

No, in France they do dating scans and tell you a date of conception from which they calculate. In Greece they go by date of implantation a week later which can cause confusion (well it did for me going between the two countries!!!).

Congratulations OP!

WeOnlyPlannedTheFirst Sat 04-May-13 22:16:31

I read somewhere that in Europe (maybe France) it is usual to think of a due month rather than a due date. I can see how that helps stop people getting hung up on a specific date and all the people hassling for news of twinges when you're just one day 'overdue'.
Regardless of the date you are given your baby is going to come when it wants to. Hopefully not too early but if your due date is 10 days before Christmas then a Christmas baby is a possibility. If your due date is middle of January a Christmas baby is still a possibility!
OP - Congrats on your pregnancy and enjoy it. I'd suggest getting a good pregnancy week by week book - they're very educational plus it's fascinating learning how your baby develops over the pregnancy. It was my regular Sunday treat when expecting my first to sit and learn he was the size of a plum etc!

pinkteapot Sat 04-May-13 22:14:48

Apple, its always ok to ask questions and wise to try find things out. I think what I found a bit funny was the phrasing of the question, mostly the assumption that the gp had "deliberately" given wrong due dates, as opposed to mistakenly done so or simply done something the OP hadnt understood (which is as it turns out). just sounded like the OP had made her mind up gp was in the wrong.
.. Anyway, mountain out of a molehill at this stage.

Christelle2207 Sat 04-May-13 22:03:20

ps day of implantation, typically a week or so after conception, doesn't come into it at all. As others mentioned you could have ovulated several days before you conceived.

Christelle2207 Sat 04-May-13 22:00:39

OP just to make it clear that in the UK pregnancies are calculated as 40 weeks long despite the fact that there are only 38 weeks between conception and due date - i.e. you spend the first two weeks of your pregnancy NOT pregnant. This is based on average women conceiving 2 weeks after the first day of their last period but up to a week either side of this will be common.
As others have said your scan will give you a more precise due date.

Bodicea Sat 04-May-13 18:34:30

Also you never know for sure date of conception, sperm can survive up to four days in body so can conceive much later than when you had sex. That's why lmp is more accurate than conception date x

Applepiesky Sat 04-May-13 16:50:59

Think a few of you are being rather harsh on this lady. She has already explained she is a first timer, as am I, and although I knew how due date is worked out, there's a HELL of a lot I don't know. Hence the reason for these forums, for people to be able to ask questions, get help and advice. No need to accuse her of being accusatory when she is just looking for reassurance! Have noticed this a lot on here, people can be so quick to judge and often respond to some people most negatively!

Gonnabmummy Sat 04-May-13 15:01:11

Pregnancy is dated 40 weeks from first day of last period it's most accurate way albeit 2 weeks either side anyhow. Most women know for definite when last period was and conception can happen at diff stages

MummyBurrows Fri 03-May-13 16:03:10

First off- Congratulations!! [Grin]

Secondly- I really wouldn't worry about when the doctor says your due. The due date will change with every scan you have anyway! FWIW I know full well I didn't concieve my current pregnancy anywhere near the time my gp said,I also know that I didn't concieve on the dates either my early dating scan and 12wk scan gave but the weeks thing is just to make it easier for scans and midwife check ups and telling people when they ask "how far gone are you?" really,they're very rarely accurate. We all know that most babies arrive anytime between the 38-42wk mark on average and that "due dates" are nothing but a rough guess meaning "sometime around that date but we don't actually know,it could be a week or 2 either way" will come when he or she is ready so don't obsess too much over any due date you get given,just make sure you're ready with a hospital bag by the door,I personally have mine ready by the time I'm 30wks-just incase!xx

Startail Fri 03-May-13 14:59:40

They still try to go from date of last period even if you've had IVF and know precisely when the baby was conceived.

Drove DF nuts trying to explain that 38 weeks after conception was a more accurate date than 40 weeks after her last period.

knittingirl Fri 03-May-13 14:51:13

The thing is, even if you know which act of sex made the baby, you still don't know when fertilization occurred. Sperm can hang around in the uterus/fallopian tubes for up to five days, and the egg lives for about 24 hours from ovulation. So you could have sex at any point within a six day period, and still "conceive" on the same day, if that makes sense.

Hence, they go with lmp as an approximation, then date you properly at the 12 week scan.

Fenaklu Fri 03-May-13 14:20:59

Thanks people (esp midori1999 and mrsden) - for some reason I was thinking that the due date was calculated from fertilisation of the egg rather than implantation which is why it didn't make sense that the known date of sex was ignored - I always thought they calculated from the last period only if they didn't have a reliable date for conception!
And for those asking why I didn't query it at the time - it was only just now I realised that the dates didn't seem to add up - my mind was going round the SH*T I'M PREGNANT hamster wheel at the time!

HoneyDragon Fri 03-May-13 14:13:33

Yup. On both my conception "dates" my dh was out the country grin <<hussy>>

ShowOfHands Fri 03-May-13 14:06:33

Your due date is largely meaningless in terms of when your baby will arrive. It's just an aid to appropriate care. A normal pregnancy lasts between 37 and 42 weeks so you have a large window really. And a Christmas baby is a bit special. The calculation from the last period gives a rough, inaccurate guide, first scan gives a much better guide and then the baby comes when it wants anyway. grin

Have you got any decent pregnancy books?

kilmuir Fri 03-May-13 14:03:14

If you go 2 weeks over you could be in hospital opening your Xmas pressies

TeamEdward Fri 03-May-13 14:02:50

Message withdrawn at poster's request.

serin Fri 03-May-13 13:59:58

grin it will come when its ready!

AnythingNotEverything Fri 03-May-13 13:58:08

Also, conception doesn't necessarily happen on the day you dtd!

AnythingNotEverything Fri 03-May-13 13:57:10

Your due date is just a guide anyway - and is a guess really until you get some scans.

I read somewhere that only 7% of babies are born on their due date.

This is the first of many steps where you'll see that pregnancy, childbirth and midwifery are not exact sciences.


mrsden Fri 03-May-13 13:56:41

because that's how pregnancies are dated in the UK. There has to be a standard system in each country, it makes little difference what that system is so long as everyone is using the same. Ovulation is not a great one to use because most people don't know when they ovulate, and even knowing when you ovulated it's not possible to know exactly when conception happened. The vast majority will know the date of their last period so it gives a good starting point. There will be a revised date after the first scan if the size is out.

midori1999 Fri 03-May-13 13:56:33

Because that is how gestation is calculated. They can't calculate it one way for some people and another way for others. Plus, you don't know the exact date of conception, because even if you know the date you had sex, you will not necessarily know the date you ovulated or implanted. If there is any difference from the date calculated by your last period, you will find out at your dating scan.

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