Can an ultrasound be wrong about how far along i am?

Krista - posted on 11/28/2010 ( 13 moms have responded )

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when i first went to the doctor they went by my last period and then i had an ultrasound and said i wasnt as far along as they thought. right now they say im 28weeks but according to my period im 31. and i was almost positive about the day i concieved. could the ultrasound be wrong? they just go by weight and height, and my daughter was a small baby so mabe he is too and it just looks like im not as far? also i have been having contractions, and that would make more sense if i was further along.

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Meei - posted on 11/29/2012

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yea i should be 32 weeks but the doc said iam 30. did your baby camed out on the right date that the ultrasound did or was it wrong ?

Sneaky - posted on 11/28/2010

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I ended up having three different due dates for my last baby - I had three ultrasounds and all were WRONG! Bub ended up arriving on the exact date I had calculated from my LMP, so my advice is to go with your dates and ignore the ultrasound. FYI, at my last ultrasound the tech told me that the ultrasound was accurate +/- three weeks, so if the ultrasound says that you are 28 weeks, then that could mean that you are really either 25 weeks, or 31 weeks or anywhere in between. I have never understood why ultrasound dates are taken so seriously when they are so inaccurate!

Kelly - posted on 11/28/2010

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I had the same thing with my first pregnancy, Don't doubt yourself, if you know when your last period was and you were trying to concieve, then your prob. right on the dates, this happend to me 22 years ago with my first child, and it ended up being Fetal growth retardation, it sounds worse then it is, my baby was just growing a bit slower then normal, he is a helathy 22 yr. old that is 6' 1 and 150, still a bit skinny, but healthy. Might be something to mention at your next apointment, also my son came 2weeks late, doctor didn't want to mess with nature, thank goodness he was only 6 lb 8oz. hope this helped.

Jessie - posted on 11/29/2010

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I would just trust your own measurements and instincts. I only had the one ultrasound (at approx 21 weeks) and they said he measured smaller than my due date by a week, but the didnt move the date... my son was just small as am I. He came on 7/13/09, a week before his orginal due date (7/20/09) and all along the doctor had been telling me I would probably go over my due date and go into august. This was based on 1)the ultrasound, 2) he is my first child, and 3) my stomach always measured small. He was just a a small kid and at 16 months he has always been in the 10th percentile or under. Of course those numbers are based on formula fed children, which he not, but that's what they go off of so...

Nicole - posted on 11/28/2010

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In my ultrasound they measured the femur bone and said I was 32 weeks but according to my previous ultrasound I was 30 weeks. I also got an EDD of 09/11/10 from the date of my last period and an EDD of 09/23/10 from my first ultrasound. Somebody entered the info into the computer wrong so they thought I was overdue and induced me on the 22nd. Come to find out I wasn't due til the next day!

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Lacye - posted on 11/29/2012

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I would go by the earlier ultrasounds. Once you reach a certain time, all babies start developing differently. Some larger than others. I am currently 30 weeks (will be 31 weeks Saturday) and my son is measuring 2 weeks bigger than he's supposed to be. Just go with your gut. He will come out when he's ready anyways. :D

Jodi - posted on 11/28/2010

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"I find it strange for an ultrasound to be that far off on dates."



@ Amanda, they thought mine was 4 weeks out.....it IS possible. I had several ultrasounds that showed the same thing. In the end they just decided she was extremely small, and they were right, she was born in the 5th percentile at full term. She was smaller than many premmie babies.



I would ALWAYS go with a due date from an earlier ultrasound, or your own dates, than a later ultrasound.

Krista - posted on 11/28/2010

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ya my doctor went by my the first date of my last period but when i had my ultrasound, they changed my due date to match what the ultrasound had said

Amanda - posted on 11/28/2010

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It's not uncommon to be off by ultrasound. It's not an exact science and can be off one way or the other. Ultrasound techs can't predict sex of the baby or size exactly either.

I knew exactly when I concieved my son, but they went by date of first missed period (FMP) which put me due middle of november. My son was born end of october, exactly when I predicted based on conception. Ask your doctor if they go by first missed period, last menstrual period, or estimated conception date when they estimate due date. If they base it off of ultrasound, those are usually estimated by dates based off of statistical FMP dates.

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Well it makes sense to me that if you're positive about the day you concieved then you're probably right about how far along you are, especially if your previous child was small too. Have you told your doctor that you know the date you concieved?

Krista - posted on 11/28/2010

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im sorry i had that wrong, i'm 28 weeks now but according to my period im 31.

Amanda - posted on 11/28/2010

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27 weeks This week, your baby weighs almost 2 pounds (like a head of cauliflower) and is about 14 1/2 inches long with her legs extended



32 weeks By now, your baby weighs 3.75 pounds (pick up a large jicama) and is about 16.7 inches long, taking up a lot of space in your uterus.



I find it strange for an ultrasound to be that far off on dates. When did you find out you were pregnant (at what week)?



Lots of us woman have had doctors off by 2 weeks one way or another but 5 weeks thats a whole period, and very strange to be that far off.

Jodi - posted on 11/28/2010

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The earlier the ultrasound, the more accurate it is because of the indicators. A bit later, they tend to go by size. They were really wrong with my later ultrasounds because my daughter was very small. My first ultrasound was at 10 weeks, and all the indicators showed I was actually 10 weeks. Later on, they thought I was actually not as far along as I was, simply because of her size. They thought we were a month out. Go by your initial ultrasound.

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