Can an EDD on an ultrasound be dating the pregnancy from

The EDD in an ultrasound is basing the due date on the fetuses size rather than any particular marker such as conception. You will see, the more ultrasounds you have the EDD will change a couple days in either direction.

Technically, the EDD is truly based on the first day of your last period and add 40 weeks. There is no science that can tell you the exact day better than one with a 2-3 day deviation. Sperm travel varies about 48 hours making it nearly impossible to pinpont an exact moment.

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Shyla RN

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why when you put information on the computer such as your due date it calculates your date of conception? If you actually did conceive on the 28th of december the numbers on the ultrasound wouldnt really show that day anyway it would be a little bit further along like maybe the 3 or four days ahead because the process takes a few days anyway, right? From conception, fertilization and implantation?

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The ultrasound may not show the 28th of December because it is basing the date on how old the average fetus is when it is the size of yours. Its only an average and not exact because everyone grows at a slightly different rate but, it can be close enough like by a couple of days.

There are so many ways to calculate due dates. The date of conception can be averaged from a last menstrual period because the average women will about the same time but, it changes from woman to woman and cycle to cycle. Same reason why the doctor will tell you having sex without protection during your period, even if it is assumed you are not going to be ovulating. Is not a safe method of birth control. Some women can and do ovulate during their period as well as any time within the month. This is also why its safer to estimate a due date from date of last menstrual period, it eliminates the variety and has a concrete time.

Most people don't like to think in these terms because it means you are pregnant for 10 months. You technically are but, when you think in 9 months, it doesn't consider the first two weeks between your period and conception(fertilization is the same as this) and it thinks in terms of calendar months. There is no calender month that is only 4 weeks except February. All those missing days between day 29-31 in some months add up.

So basically, its the same, 9 calender months, with the first day being conception, or 40 weeks which is really 10 28 day months first date being first day or last menstrual period. Figuring 40 weeks out tends to be more accurate.

Shyla RN

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yes

my last question is than if on know my lmp as 12/09/2005 why wouldnt he use that date in his fondings at all. I also know my date of conception as 12/24 . The ultrasound tech says i am worng with my dates because at my ultrasound on 4/26 she showed me at 15.3 cent instead of 16? I thought babies can and will grow diff and that 1/2 cent would not really be a big deal.

Are you figuring date of conception to be a date of intercourse? If so, you could be off by a few days. Sperm stay alive up 72 hours in the womb and may have been taking their time to actually get to the egg. Date of conception is the date the sperm enter the egg.

1/2 centimeter is a big deal when you are that far along. But, ultrasounds are subjective and have room for user error as well. Your doctor may not be considering LMP in your case because you are much more exact with your timings than most patients. If most patients were as good as you at being a self-historian, it would make my life easier. Plus, its almost exact for 14 days, 2 weeks from LMP to self-documented conception.

Shyla

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yea actually if intercourse was on the 24th i had the implantation bleeding on the 28th so according to the computer saying that i conceived on the 28th if due on sept 21 i guess that would be right because that bleed on the 28th was exactly 5 days after intercourse and they are dating against that day

Edited by Customer (name blocked for privacy) on July 21 2006 at 4:58pm

I don't think you conceived on the 28th, more like late 26th-27th. It takes the fertilized egg about a day or two to travel to the uterus. Plus, sperm don't last 5 days. I think that is due to microscopic measurement error on the part of the tech. A millimeter is easy to misinterpret.

Shyla RN

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so being that i remember having intercourse on the 24th (sad but true) that i remember this date the sperm probably traveled and took its time to fertilize, maybe the 26th or 27th? The bleeding thar i had on the 28th i am taking as implantation and the major ultraound at the hospital had said a due date of sept 19th which is probably about right. Does that sound about right to you ? I just want to say thank you again for all of your help .

That does sound right, it couls been a little sooner but most likely not until the 26th.

Your welcome, glad I could help!
Shyla RN

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