Ultrasound Question??

Question

Alright, I know my LMP date was definitely 8/23/06. DOC should have been approx. 9/8/2006.

First ultrasound on 9/29 dated me at 5 weeks or less, because it was soooo small.
Second ultrasoud on 10/13 dated me at 7 weeks 1 day.
Third ultrasound on 11/14 dated me at 12 weeks 1 day.
*Don't worry, only one more ultrasound for me.

All the dates are only a few days off of each other, but I was just wondering which dating is the most accurate?

Thank you for responding!!!

=)

Answer 1

I am an ultrasound technician at a Women's Hospital and I specialie in OB/GYN ultrasound.

The eariliest ultrasound is the most accurate, providing an embryo was seen. If the first ultrasound revealed only the presense of a gestational sac, without the embryo, the dating of the pregnancy would be postponed until the embryo was seen.

Once an embryo is seen and an accurate CRL (Crown-Rump Lenth) is obtained, the dating of the pregnany is calculated. If you have a sure LMP (last menstrual period) and the ultrasound is consistent with the LMP, your dates do not change.

The accuracy of ultrasound for dating is directly related to the gestational age at which the dating measurements are obtained. For instance, at 6 weeks, ultrasound is accurate to within +/- 0.4 weeks (about 3 days). At 10 weeks, ultrasound is accurate to within +/- 1.0 weeks (7 days). At 15 weeks, ultrasound is accurate to within 1.4 weeks (10 days). By the third trimester, ultrasound is accurate to within only 2.2 weeks (about 16 days).

So as you can see, the older the gestation, the less accurate ultrasound is for dating. Some of the reasons for this are as follows;
1. first trimester embryos typically measure within a couple milimeters of the typical embryo.
2. Later, family genes, nutrition, gender, maternal size, firt pregnancy, ethnicity all play an important role in the size of a baby regardless of conception date. (Think of it this way: you look at two newborn babies side-by-side; conceived on the same day, born on the same day; one is 10 pounds, the other is 5 pounds. Both are healthy yet their sizes differ dramatically)

Once accurate dating is established the gestational age and due date should NOT change with each additional ultrasound exam. Changing the gestational age would make every fetus measure in the 50% (roughly). In other words; changing the dates to match the size of the fetus would make a fetus which is too small appear to be growing properly OR a fetus which is too large appear normal sized. Also, if a fetus which has had accurate dating in the first trimester is suddenly measuring a month larger and the dates are changed, the fetus would risk being delivered too soon, when the lungs have not matured--- only because of the size of the baby.

With a sure LMP and a regular period, the dating would be changed to that calculated by ultrasound only if the gestatonal age by LMP conflicted with the ultrasound composite gestational age outside the accuracy rate.
I hope I have helped.

Answer 2

the standard ultrasounds are 'reasonably safe' meaning they don't pose a 'significant' risk to the baby. The benefits basically outweigh the risks. Nevertheless, you shouldn't have ultrasounds unless needed as they definitely are not without risk. Remember years ago they also thought x rays were safe.. nowadays at least most doctors do tell you about the risks of ultrasound. At least mine did. Four is still within safe limits. But stay away from those new 3D ultrasounds.. they use a mega dose of ultrasound and they are NOT safe. There has been much controversy and many places are refusing to do them, only the more profit orientated places. Go ahead and have this ultrasound... four is ok.

Answer 3

Is the doctor scheduling all of these ultrasounds? what's the big deal about how far along you are? I never had an ultrasound to see how far along I was until I was 19w! All you have to know is when was the first day of your last menstrual period is and they have a little chart that tells you aprox how far along you are. In my ultrasound at 19w, the due date matched perfectly well what the doctors had told me the first time. I developed high blood pressure so I had to have another ultrasound done at 28 weeks to make sure the baby is growing well, and everything is fine, except for the due date, that has been changed one week early. If I were you, I would wait until you are farther into the pregnancy because it depends on how your baby is growing inside of you that the due date will either remain or change. Babies are unpredictable so you should wait until you are at least 20 weeks to do another ultrasound, other wise your due date will be changing all the time, and plus it also depends on how experienced the technitian is doing the ultrasounds, sometimes they won't meassure the baby correctly and that affects the scan too. Just relax and wait, you will be pregnant for a while. Go with your last menstrual period for now.

Answer 4

well, if the dates are only a few off from eachother, that's not too bad. Even when you know your LMP, that doesn't necessarily mean that you ovulated at exactly the day your Dr. said, so your DOC could have been a few days later than you thought. Usually the first few ultrasounds early on are the most accurate... meaning that the later ultrasounds (4 months and on) are less accurate for determining the age and weight of your baby. I would trust what your Dr. is telling you... the dates certainly can change in the first few months.

Good luck!

Answer 5

My Doc told me that an ultrasound done around 9- 12 weeks is usually the most accurate for determining your due date. So I am guessing that your last ultrasound was in this time frame. The due date that they gave you at the last appointment is the one that I would stick with. Good luck to you!

Answer 6

The first ultrasound is the most accurate. That is what my OB told me and actually I think it is because the dates match up for me.

Answer 7

LMP is always the best indication, babies grow at slightly different rates, and no two babies are the same so US dates may always be a little out, especially if bubs had a growth spurt that week!

Answer 8

the first ultrasound is the most accurate. it is 98 % accurate. i had many similiar US and i asked which one was accurate and the tech said the 1st one is always the most accurate.

Answer 9

the earliest ultrasound would be the most accurate.