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Yes, don't worry about the difference.

By 4 weeks, a fetus cannot be seen but the thickening of the uterine lining can be detected. By around 5 weeks, an ultrasound can almost always confirm that you are pregnant.

Between four and a half to five weeks, the gestational sac is easily seen and can be measured, since the average growth is 1mm per day at this time but not completely uniform this information is considered a tentative date when LMP date is not known.

A few weeks later Ultra Sound to determine fetal age is done by taking a measurement of either the femur (longest bone in the body) or the crown of the head to the pelvis called the "crown rump". The measurement is taken and automatically then by comparing your baby's measurements to the data from a large collection of measurements, the ultrasound can then tell how far along your baby is.This is most accurate between week 7 and week 14.

Doctors have fallen into using a rule in ultrasound that when the due date based on ultrasound doesn't vary from the mother's dates by more than a week, stick with the mother's dates; if the ultrasound disagrees by more than a week to ten days, it becomes wiser to rely on the ultrasound.

Later in pregnancy other things such as babies who are larger than average size, babies growing at different rates among pregnancies, will cause inaccurate dating of pregnancy. But are still an excellent tool for other issues that may develop.

The bottom line is, Ultra Sound is a machine made and run by humans, it is an amazing tool for many things, but babies are still going to come into this world when they are ready, regardless of dates. Only 5 to 10 percent of babies arrive on their due date, whether the date is by ultra sound or LMP.

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โˆ™ 2015-07-15 20:51:55
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Q: Can a ultrasound not be accurate by a week or so in determining how many weeks you are pregnant?
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Related questions

How accurate are ultrasounds in determining when you conceived?

At 7 weeks an ultrasound is accurate within 2 or 3 days. At 20 weeks it is accurate within 5-7 days.


How soon can a ultrasound tell if your pregnant?

You can tell you are pregnant through ultrasound as early as 4 weeks with a vaginal ultrasound.


The ultrasound said that you were 12 weeks and 1 day pregnant how accurate is that?

as accurate as you can get. they told me with my 3rd baby that I was further along then we thought,and she was born the day they predicted.


If ultrasound said you were 4.5 weeks pregnant when did you get pregnant?

Around 2.5 weeks ago.


Can an ultrasound be off by a month in the first trimester How accurate is an ultrasound at 7 weeks?

Well I had an ultrasound at 13 weeks and it was not very accurate. and it will not be able to tell the sex of your baby. Oh by the way, depending on what kind of insurance you have and what hospital you are at you may not get another ultrasound. An ultrasound at 7 weeks is extremely accurate, within 2-3 days. At 13 weeks it will be accurate within about 5 days. It can certainly not be off by a month.


How off can an ultrasound be that estimated your last menstrual period the same at eight weeks and twelve weeks?

I think this is what you mean. For example. On 28th December the ultrasound said you were 8 weeks pregnant, then on 25th January it said you were 12 weeks pregnant. This would be accurate to within 4-5 days each time.


If the ultrasound shows you to be 26 weeks pregnant is that when you got pregnant 26 weeks ago?

Yes.


Can an ultrasound tell you exactly how many weeks and days you are pregnant?

It's not an exact science, but it can give you a pretty good idea. the less pregnant you are the more accurate it is. ~pawsalmighty


Can a ultrasound be accurate if its saying im now due 3 weeks later then they determined?

Can a ultrasound be accurate if its saying im now due 3 weeks later then they determined?


When did you conceive if your ultrasound says you are 8 weeks pregnant?

8 weeks ago


If you went to the doctor and they did an early ultrasound and said you were 5 weeks and 3 days pregnant could you have an early ultrasound at 3 weeks and 3 days pregnant?

There would be no gestational sac visible @ 3 weeks. YES At 5 weeks 3 days pregnant by ultrasound, you conceived 3 weeks 3 days earlier.


Very irregular menstrual cycle your first day of lmp was aug 28 2005 today on October 13 2006 you are currently 41.5 weeks pregnant according to an us done at 9.2 weeks how accurate was that date?

A baby grows at a very precise rate in the first 12 weeks. A very accurate date can be given as long as you have an ultrasound under 12 weeks. If your ultrasound was at 9.2 weeks, I would consider this accurate.

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