How accurate is an eight week ultrasound?

Question

When you have eight week ultrasound to date pregancy, what happens to the two week factor as when using you LMP to calculate due date? If ultrasound says you are eight weeks, is that the age of fetus from time of conception???

Answer 1

If they told you were 8 weeks than that is how far along you are in total. It is dated from the first day of your missed period.
but you will find that in most cases it wont be the same as your dates. as they just use a scale to say how big the baby is to determine how old the baby is. It should be within 1 week of your last period. It depends on when you ovulated. eg if you don't ovulated until The 18th day in your cycle than the scan would show that your last period was 4 days later than it really was.

It is all based on the average person. this dose make it slightly inaccurate as everyone is different.
early ultrasound is said to be much more accurate at dating pregnancy (compared to later on) as all foetus develop at the same rate until 14weeks. Than genetics and other factors effect the size of your baby.

Answer 2

Docs measure from your last period date not time of conception since there is really NO way to know when you ovulated and/or concieved. It's easier to guage size etc from the last known menstrual date... note that this also means baby can be gestationally 7 days either way and is not exact because of this, depending on if you ovulated late, or early in a standard 28 day cycle. They will measure head circumfrence, Femer Length and abdomen circumfrence and compare to a chart of known fetal measurements to come up with an approximate date. They've gone back and forth so many times on due date for me I know i'm due sometime after February, but really no idea when. The earliest date I have is the 4th and the latest date I have is the 10th.

Answer 3

No, if ultrasound says your are eight weeks, the age of fetus is 6 weeks.

Answer 4

the ultrasound is more accurate, it's from the time of conception-they will give you your due date based on that. They measure the fetus and can tell. My son was measured at 10 weeks and again at 21 weeks-the due date never changed based on that-he was actually born (without induction) on his due date!

Answer 5

The fetus would actually be 6 weeks old. I had an ultrasound at 10 weeks w/ my first baby, so she was 8 weeks old and we could see her clearly. She looked like a little alien. : )

Answer 6

a few years ago we rescued a pregnant lab. she never really looked pregnant. I thought one or 2 pups. She had 9 all very healthy, beautiful pups. I would think if there was only one pup that she would barely show. most pregnancies do not become apparent to the eye before about 5-6 weeks along. It is very unusual for one to start showing at 3 1/2 weeks. I bet there are more pups than one, or she may be carrying some dead ones.

Answer 7

Listen to Mcollum she is right . and an eight week ultrasound is very accurate. the earlier you get your ultrasound to date your pregnancy the better the results. COming from someone who didn't find out until 13 weeks!

Answer 8

early ultrasounds are generally very accurate, its later in pregnancy when the ultrasound is less accurate. Not sure about all the technical things, but all of my early ultrasounds were accurate, 1 to 2 days off.

Answer 9

Even when the doctors come up with their assessment of the age of the fetus, they are still going off of LMP. Because they take an average of all 8 wk fetuses (judging by LMP) and figure an average in height, weight, head circ etc.

Answer 10

It's accurate; but not as accurate as a 20 week ultrasound