Medical Questions > Pregnancy Forum > Pregnancy Calendar Conception : When did I Conceive ? Forum

Ultrasound series & conception/due dates

Hi,

I am wondering how accurate ultrasounds (or a series of ultrasounds) are at dating a pregnancy. My LMP was the beginning of May but my cycles were irregular. I skipped the month of May. No clue when I ovulated. I had sex on May 28 and then again on June 4/5. A pregnancy test on June 14th at dr office showed negative. A test finally taken on the 23rd showed positive. I was unsure about dates so the dr gave me an ultrasound on 7/6 showing me at 5w3d (only showed yolk sac and g-sac which would have given me a due date of 3/4 or 3/5 but they didn't use this date b/c no fetal pole). I had another on 7/18 showing 7 1/2 weeks, which showed fetal pole and heartbeat and gave me due date of 3/2/12. I had a third ultrasound on 7/25 which showed me at a little shy of 8 1/2 weeks and would have given me a due date of 3/4/12 but they stuck with the 3/2 date since that was the first with a fetal pole. I also had another ultrasound at 12 weeks exactly (according to 3/2 due date) and fetus measured 12w3d.

How accurate are these ultrasounds with dating and how likely is it that all these are off? All ultrasounds done by different techs; the 12 week done by perinatologist. Is the conception definitely the June date? Your help is appreciated thank you.
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First Helper kristigraham
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replied September 22nd, 2011
Community Volunteer
The ultrasound at 6 weeks is the most accurate - to within a day or two. From there it gets less and less accurate. At week 18 it is only accurate to about 8/9/10 days. After that it cannot be used to determine conception any more because other factors will influence the baby's growth.

That is the reason why they are sticking with the 3/2 date. You can also use the average date for the 2nd and 3rd scans, 3/3.

Sex between June 4 and June 14 got you pregnant.

Best of luck!
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replied September 22nd, 2011
Thanks for your input. I've read that ultrasounds can be a week or two off but I don't know how that couldve been off by a week or two at 5w3d! Just making sure I wasn't missing something because if the baby was conceived at the earlier date then it was apparently not growing right.
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replied September 23rd, 2011
Determining Conception Date
For me it was the same. Im not sure about my conception dates. I had sex on 30th July and then again on 14th August. My LMP was just spotting and it ended 27th July. The Ultrasound that I did on 16th Sept put the GA (LMP) at 7 wks and the GA (AUA) at 6wks 4 days (does AUA mean the actual age of the fetus after conception?). When would be the most likely date I would have conceived in?
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replied September 24th, 2011
Yes the GA is the gestational age of the fetus, which starts at conception...it looks like you conceived on July 30th date...basically if you count back 6w4d from your ultrasound it looks like it's around 7/30 to the day...so I guess it sounds like your ultrasound was pretty darn accurate! Does that make sense?
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replied November 6th, 2011
when did i concieve
I can't remember exactly when I had sex but I spotted a little towards the end of may and no menstrual in June I fount I was having twins and their due dates were scheduled for Feb 17 2012 I went back for ultra sounds && my date changed to March 2nd is this accurate if so when did I concieve???
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replied March 14th, 2012
help plz
can anyone help me please.. i had a scan on the 7/1 and i got told i was no more than 4weeks.. i then had a scan on the 11/1 and got told 4-5 weeks.. i had a scan on the 20/1 and i got told 6 weeks 3days. i had a 14week scan on 13/3 and i am 14weeks/3 and due on 8th Sept does anyone know when i conceived.. i really need help with this
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replied March 16th, 2012
to tack 92, gestational age is NOT age since conception. age since conception is fertilization age. gestational age is 2 weeks older than fertilization age.
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