Ultrasound and EDD dates.?

Question

Ok i am confused as to how ultrasounds measure the EDD.

My LMP was Sept 13, 2007.
My average cycle is 32 days.


According to this i am getting a due date of June 23rd 08
Making me be 8 weeks 6 Days along.

When i had an ultrasound at about 6 weeks, it showed instead
at about 5 weeks.

Now i had an ultrasound today, where i am showing 8w6d along
and the ultrasound showed me at 7w 5d. About a week behind too.

So here is what i want to know, when you measure your EDD
from your LMP, you in essence include two weeks where there is no baby.
(give or take 2 weeks because some people ovulate later or earlier)
But what does the ultrasound measure? The baby from conception?
or the baby from the last menstrual period?

If the baby is 1 week behind because they dont measure the first two weeks of the period
then i either ovulated earlier or i can add two weeks to that date.
Otherwise it makes no scence to me because then the date of conception is bascially
the same date as when i took ap regnancy test, and i wouldnt show pregnant
on a test on the day of conception, or 1 or two days after it.

So what does an ultrasound measure, form LMP or from Conception?

Answer 1

You can't rely on your LMP because you don't know when you ovulated. According to my LMP I should be 15+2 but I have had 3 scans all with the same EDD making me 13+3. I simply didn't ovulate at the expected time. Babies generally come 2 weeks either side of the EDD with first time babies being notoriously late!!!!
I would trust your scan and prepare for the baby with that EDD date.

Answer 2

The ultrasound generally measures from LMP, just as you and your doctor have. For the measurements to be one week behind is not unusual at all.

Sometimes, though, it will simply measure gestational age which would be more like from conception. You can ask your doctor or the technician who did the scan which method they are using.

But consider yourself 8 weeks along instead of 7.

Most women deliver within 2 weeks of their "estimated due date" and this is all within the normal range. It's not an exact science. And most babies rarely measure perfectly to the number of weeks you are.

My ultrasounds AND my tummy measurements (in centimeters) have always been 1-2 weeks behind where I knew I was. My calculations were correct and the babies were all on time (and healthy weights) according to the LMP calculation.

Answer 3

Im not sure if they measure from lmp or conception but with my 2nd working out from my lmp i gave myself a date of 5th (ish) of september and when the midwife came round she worked out a date of 30th aug from my lmp but when i had my scan they gave me a final date of 26th aug so he was nearly a week earlier than they first thought and nearly 2 weeks than wot i thought. they do take into account the 2weeks or so after your period for ovulation but not every ones cycle is 28 days and some people can ovulate early or later.

Answer 4

The ultrasound date will include the 2 weeks.

I just looked back at some of mine and what is actually PRINTED in it says gestational age. If yours says that then it;s from conception.