Can a first dating scan at 12 weeks be off by 2 weeks?

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All forms of dating can be off plus or minus two weeks.

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Originally Posted by J_9

All forms of dating can be off plus or minus two weeks.

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Our Dr is adamit that they can only be off 3-5 days at the 12 week scan when determining gestational age.. is that inaccurate?

Not really inaccurate. However all of dating is nothing more than an educated guess since we don't know exactly when the sperm met the egg.

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Originally Posted by J_9

Not really inaccurate. However all of dating is nothing more than an educated guess since we don't know exactly when the sperm met the egg.

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Our due date from lmp was march 17th and changed to march 24 after 12 week dating scan.can you help me narrow down a time frame of probable conception?

I use the same wheel that your doctor uses to determine dating. But I need the LMP to do that.

With the dates you have given me conception for the March 17 date would be right around June 24. And with the date of March 24, I get a conception date of about April 1.

You see dating is an inexact science. It is based on a strict 28 day cycle and consistent ovulation. Not all women have a 28 day cycle every month of the year throughout their lifetime and not all women ovulate the same time every month. Ovulation days can vary. Sperm can live in a woman for up to 3-5 days before meeting up with the egg in the fallopian tube, thus making calculations more difficult.

Since we don't have a camera in the ovaries or the fallopian tubes to know exactly when the sperm met the egg, we had to create a mathematical formula to determine dating. That mathematical formula is identical for every woman no matter how close together or how far apart their cycles/ovulations are.

That breaks it down really well.I really appreciate your response. When they estimate gestational age does that give age of fetus from conception or age from conception plus two weeks.. I've read both?

Lmp June 13

To be more specific I'm trying to rule out intercourse that accured may 31.. I think my answer is very obvious since it's a while month apart just wanted apros opinion..

The lmp was June 13 which gave a due date of march 17 when we had our dating scan at 12 weeks the Dr said the fetus was measuring smaller by one week which moved our dates to march 24. Which we figured they would move it due to a approximate guess on lmp. We have done all the calculators possible and they all put us conceiving at end of June beginning of July.. can we be certain it wasn't from intercourse on may 31 ? Which was a whole month ahead of our ultrasound dates? Thanks in advance

Dating may be off up to perhaps 2 weeks, I do no see how it can be that much earlier. Is there a reason that a conception date matters?

Because I just found it the meds I was taking then wasn't out of my body until the end of may. Just wanted to be assured that it was from end of June when I was med free.. just for personal reasons. I think is very clear that its not from end of may, but just wanted a pros opinion

Should be clear, really does not look like it could be that much earlier.

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Originally Posted by Fr_Chuck

should be clear, really does not look like it could be that much earlier.

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Thank you!

Are you the man or the woman?

Man

What medication were you on that might hurt the fetus?