How accured are the transvaginal ultrasounds?

Okay today  i found out that im 11 weeks and 2days, i had an transvaginal ultrasound. I was wondering if that means that the date i actually concieve (conceive) the fetus was actually on the 19th of june? But the 1st day of my last period was the the 15th of june. So does this mean that the ultrasound is off by a week possibly? And is it possible that it is off by 2weeks?

[christa111]

im not quite sure of the answer but the scan is the most accurate for dates. i had a transvaginal ultrasound at 7 weeks but it showed i was only 5 weeks. they told me i conceived later than i thought i did. i am now 8 weeks 1 day.

[ldc03]

Humm...thats weird...so that makes you only 6 weeks, so the ultrasound was off by 2 weeks than?

[mj_mommy_manda]

implantation doesn't take place until 2 weeks after fertilization and that is when the fetus starts developing.

[peekawho]

Pregnancies are dated by menstrual weeks.  As an example, if you are told you are 8 weeks pregnant, you have actually only been pregnant for 6 weeks.

The count begins from the first day of your last period, and since you were not pregnant then, but usually conceive 2 weeks later when you ovulate, it adds two weeks to the pregnancy.  Pregancy lasts approx 40 weeks from your last period...but in actuality, you are pregnant for 38 weeks (again, more or less)

Transvag ultrasounds, done early in pregnancy, are the most accurate.  If done in the first trimester, they are accurate to within a few days either way.  later in pregnancy, ultrasounds are less accurate, because of the difference in the later growth of the baby.

Early in pregnancy, most embryos are about the same size, so sizing is more consistent and accurate.

[ldc03]

so therefore i got pregnant around july 5th?

[peekawho]

I'm a bit leary of implying exactly when you got pregnant.  Is there a question of paternity here?

Usually, you conceive 2 weeks after the first day of your last menstrual period...IF you have a 28 day cycle.  If you have a longer cycle, you usually ovulate 2 weeks before the day you expect your next period...I know, its very confusing.

If there is a paternity question going on, be honest with your doctor, and let him/her go over all the dates/sizes with you to see if a conception date can be estimated with any accuracy.  

[ldc03]

Could it be possible that i may have ovaluted earlier?