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Help me get my head arund dates...

(14 Posts)
fufulina Mon 05-Sep-11 08:40:11


I am confused, and wondered if anyone can help. I know when I conceived my baby (it was a wedding we were at; we don't have sex THAT much...), and I know the first day of my LMP. But my scans have put me eight days ahead of my dates.

In effect, the doctors have moved my LMP back by 8 days? Why do they go by size - are there no variances between babies at 16 weeks? So if the femur is x mm, then the baby is x weeks? I really don't get it. Can I ask the hospital to go with my dates - have no desire to start the induction discussions at 40 week, by my dates, by 41+1 by theirs!

Thank you ladies.

fufulina Mon 05-Sep-11 08:40:37

Sorry - head around dates. Must spell check.

CailinDana Mon 05-Sep-11 08:57:33

Actual human gestation is 38 weeks. So your baby was conceived approximately 38 weeks (give or take 2-5 days) before your due date. Doctors add two weeks to this as conception date was always calculated from your LMP which is approximately two weeks before ovulation.

fufulina Mon 05-Sep-11 09:02:21

Thanks Cailin - so why do the French consider full human gestation 41 weeks (39 by your reasoning)? And do you know re: size of babies being uniform, hence being able to date by size?

fufulina Mon 05-Sep-11 09:06:15

Sorry - just checked calcualtions, and again, it doesn't tally. My 'new' due date puts my conception (based on the 38 week gestation above) eight days before I know was possible...? Am thoroughly confused!

nannyl Mon 05-Sep-11 09:24:02

in terms of induction you dont have to be induced.

you dont have to do anything!!!!

Where i live they will NOT induce routinely until 40+14 anyway. I know my dates are also wrong (but only by 3 days). I know because i used a CBFM, OPK's + I had charted for months and all confirm my ovulation day the same day. Buy NHS i was pregnant before i ovulated lol!

Do you know for sure when you ovulated? because that can make all the difference... even if you have a 28 day cycle (like i did) you dont always ovulate on day 14 (I never did), i ovulated later and had a shorter luteal phase, so a 28 day cycle but dates arnt right for me!

Im planning a home birth (im 39+1 now buy hospital dates). Should i get to 42 weeks i will then be monitored for a few days before I let them induce me, and in the mean time, so long as everything is ok obviously, I will still be all set for my homebirth, fully supported by NHS & my midwife

fufulina Mon 05-Sep-11 09:30:20

Hi nannyl - I know when we had sex, and I tend to ovulate on day 10 of my cycle.

I have 'obstetric history' - I went to 43 weeks with DD (refused induction; had a planed c-section at 43 weeks - she was 10lbs); and vaginally delivered dead twins at 23 weeks last year, so they are hyper vigilant (which I think is ridiculous - the twins were identical, so all the history that followed was because of the fluke of a split egg, and the unevely shared planceta which caused all the problems). And because DD was big (or course she was - I was 43 weeks), the midwife on Friday said they'd want to start thinking induction at 39 weeks (!!). I know they can't force me, but I just want to understand the dating, and how they can look at my baby and say - oh because she's got a head x big, she must be x weeks...

MrsBloomingTroll Mon 05-Sep-11 12:36:06

Similar thing happened to me. My EDD was moved forward 10 days based on my scan measurements, which would have had me conceiving on day one of my cycle. 1) we only had sex one day during that cycle due to DH having an operation and 2) I was taking ovulation tests and knew I ovulated on day 11 of my cycle.

Well, DC2 arrived the day before my original due date Baedeker on LMP. The EDD based on scan was clearly nonsense! I was determined to hold out against induction if it came to it (luckily not). Good luck!

MrsBloomingTroll Mon 05-Sep-11 12:37:12

P.S. So sorry to hear about your twins x

MrsBloomingTroll Mon 05-Sep-11 12:38:51

Baedeker? Eh? IPad autocorrect strikes again!

Should read "based on".

Supersunnyday Mon 05-Sep-11 13:07:06

Message withdrawn at poster's request.

MrsBloomingTroll Mon 05-Sep-11 13:19:02

Supersunnyday's post has just reminded me that, when I got my notes back after having DC2, my EDD had been changed, back to the date based on LMP. The more accurate date.


fraktious Mon 05-Sep-11 13:23:11

In France 41 weeks is end term. Term itself is the month preceding that. Effectively if you've not delivered by your 'due' date that's when your induction is booked, usually for 3 days later (so 40+10) and they find it hard to believe that the UK let's you go over to 42 or beyond.

I thin the most recent research shows growth is only uniform to 8 weeks, possibly 12, but after that it varies too much fir accurate dating.

I was also dated wrongly and know which weekend over 2 moths I conceived!

fufulina Mon 05-Sep-11 13:55:39

Thanks all - Supersunnyday - that's what I don't get! Not all babies are born the same size, so how can dating them all on standard sizes at particular weeks gestation possibly be accurate? And they have me pregnant during my period! Odd.

Anyway - I think I'll just keep quiet until they start muttering about induction, but thank you all for your replies.

MrsBloomingtroll - I was getting all excited about a new dating method - the Baedeker method. Gutted was an iPad spell check oddity...

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