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How easy is t to get your dates wrong?

(16 Posts)
Gemz1806 Wed 27-Jul-11 14:44:43


I know the exact date of the first day of my last period, 14th June, but could I be less than 6+1?? I keep reading of people that are not as far on as they thought.

I'm constantly worrying about not being 12 weeks yet and the thought of waiting longer is driving me mad! It feels like it's taking long enough as it is!!

It's my first pregnancy and as I've not had scan yet it still all feels unreal!!

thisisyesterday Wed 27-Jul-11 14:55:07

well, if you know the exact date of your last period then you know exactly how pregnant you are surely...?

silverangel Wed 27-Jul-11 14:58:14

Pregnancy is dated by the first day of your last period but I think you could have a few days difference if you ovualte really late or really early, it wouldn't be wrong by much though if you are sure of your period date.

KatyN Fri 29-Jul-11 08:11:29

you won't get an exact date until your 12 week scan.. babies grow at the same rate until then so they can measure all sorts of stuff and work out exactly how pregnant you are. I don't think the measurements are as accurate before then, and after that the baby will grow at his own speed..

so alas you won't know EXACTLY when you concieved until then. It does make the 12 week goal a bit harder to count down too!

You are far from alone in wishing the nest 6(?) weeks to pass.. but I promise it will and then you can see the little blighter!!


firsttimer84 Fri 29-Jul-11 08:15:01

I ended up being 4 days ahead according to my scan, not sure how as we worked out we'd not even had sex that week due to being at in laws the week before christmas but hey ho! I'm not really sure how they work it out.

Hate the next 6 weeks go quickly, I remember that waiting game very well x

BagofHolly Fri 29-Jul-11 08:46:29

"well, if you know the exact date of your last period then you know exactly how pregnant you are surely...?"

How does that work then??? Date of last period tells you nothing about date of ovulation and implantation.
FWIW the dating scans are pretty accurate - I had IVF and am totally sure of my dates, and the dating scans put me 3days ahead both times.

fraktious Fri 29-Jul-11 08:58:26

We were also sure of dates (DH was only around 2 days that month) but the scan disagreed. It's possible to be a few days later because the sperm can hang around but not earlier.

Graciescotland Fri 29-Jul-11 09:05:45

I was sure of the date but I was two weeks further along when I went for dating scan, which made sense to us grin

Tangle Fri 29-Jul-11 09:11:36

The starting point for dating a pregnancy is that the EDD is 40 weeks after the first day of your Last Menstrual Period - the LMP date. This assumes that you're an "average" woman with a 28 day cycle, of which you'll ovulate on day 14. If your cycles are longer or shorter than average, or you ovulate early or late, then the LMP date will be inaccurate. LMP dating also takes no account for when the egg is fertilised (although that is generally considered to be within 24 hours of ovulation - eggs don't last as long as sperm) and when the egg implants - both of which can impact on EDD.

A scan at 12 weeks will estimate a gestational age for your baby based on measurements of head circumference, abdominal circumference, crown-rump length and femur length (can't remember if they use all of those - CRL is often the one they'll defer to if there's a discrepancy). At 12 weeks those measurements will give a gestational age with an accuracy of +/- 7 days. The error margin is because of a number of reasons:
- the latest research I've seen suggests babies only grow at a constant rate to 8 weeks, not 12.
- trying to take a 2D measurement from a 3D subject (that can move) is not trivial. The technology behind an US is good but not perfect, sonographers are good but not perfect - and even a perfect sonographer with a perfect machine may not be able to take a perfect measurement from a wriggly, squirmy baby lying at a funny angle!

The scan will be booked for about 12 weeks, based on your LMP - I certainly found that pregnancies felt a lot more believable after that point (although I do big babies so most of mine have been a day or so further along than LMP would suggest - although they don't change the EDD here unless there's a discrepancy of 7 days or more).

Whatever EDD you wind up with, IMO the most important bit to remember is that the "E" stands for "Estimated". Very few babies arrive on their EDD - which when you consider "term" for a human is considered anywhere between 37 and 42 weeks is perhaps not too surprising!

Gemz1806 Fri 29-Jul-11 15:22:27

Thank you! I feel a bit better now, I felt like a bit a idiot after posting blush but as it's my first it's all very new! I'm having a scan at 8 weeks as I had some bleeding at the weekend! Horrible thing to go through! Hopefully they will be able to tell me then what they think! smile

Thanks again!

EmJayg Fri 29-Jul-11 22:10:57

Hi I am six weeks now but according to LMP I should be 8weeks 5 days.
I had a early scan and was shocked that I was 3 weeks out. Mind you my cycle is quite long so I just got caught a lot later than I thought. Am sulking that I have to wait at least another six weeks now to hopefully feel better. I have had nausea and overwhelming tiredness since two days before I found out so pretty much felt ill as soon as I concieved lol.
Try not to worry too much, was it just spotting that you had?

Gemz1806 Fri 29-Jul-11 22:30:17

That's what I'm worried about! We will feel so much better when we get to 12wks. Hopefully it's not further away than we think. The tiredness is a killer!! Luckly I work from home so I can nap when it's quiet! And I can wear jammie trousers all day!! My belly is expanding but i think that's down to food not baby!!

Yeah the doctor thinks it was a break through bleed. We were away from home at the times had to go to a strange hospital. Stuff were lovely tho!

What did you see at your scan??xXx

Gingersnap88 Fri 29-Jul-11 22:37:41

My last period was the 27th of May so I'm supposed to be 9 weeks pregnant, however I'm only 6+5! I have irregular cycles though but yes, it is possible to be out with the dates!

sevendwarves Sat 30-Jul-11 09:23:28

I was tracking my cycle very carefully and was certain of the exact date I ovulated but my dates were still a week out. Generally a fertilised egg will implant between 4 and 12 days after ovulation, so it's easy to be a week out even if you have a 'normal' cycle.

WeLoveHaribo Sat 30-Jul-11 09:30:24

I know my exact date started last period. Doc dated me then went for 12wk scan at 14+3 to be told i was 10+1!!!!
I hav a regular but long (ish) cycle. I was devastated!!!

EmJayg Sun 31-Jul-11 11:44:54

My scan dated me at 5 and a half weeks to six weeks and It had to be a vaginal one sorry if TMI. Sonographer could see a sac and a tiny foetal pole, which to me was just a tiny white blob, really hard to see. She was excellent though and showed me a tiny rapid flicker and that was babies heartbeat. It was amazing to think that baby is 3mm yes 3mm long yet it has a heart already. I am just counting the weeks til next scan now lol

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