Accuracy of Fetal Weight via Ultrasound

mamaroar

A question for STMs or those that have already delivered..................

I will be having a growth scan tomorrow and they will estimate my little guy's weight (I will be 38 weeks +2 days).  My doctor made it clear that these can be off by up to 20% so we're just getting an "idea" of what percentile he'll be in - making sure he's not too big or too small.

Anyone have experience with this?  If so, what weight estimate were you given via ultrasound, and how much did your LO's actually weigh at birth?

lilqt3929

Lurking from February..

I had a growth ultrasound done the same day I delivered, DS was estimated to be 8lb 6oz and was born 8 hours later weighing 8lb 14oz. 

daisies05

With my second, I had an ultrasound immediately before being induced.  They were worried about low birth weight as my fluid was low. They estimated 5 pounds.  She was 7 lbs, 11 oz.  I don't put a lot of faith in "estimates" any more...

Parker16772

I haven't delivered this time but with DS1 I had a growth ultrasound due at 36 weeks and they measured him to be 4lbs 13oz. He came out at 38 weeks 2 days at 6lbs 8 oz. I would say there is no way he gained that much in a little over two weeks. I think most people agree they can usually be off either way by up to 2 lbs. 

maelic

Don't know about this guy yet, but with my daughter she was estimated to be 7lbs at 36w and was born at 41+3 weighing 9.5lbs, which was pretty close to the average gain of 0.5lbs a week late in the third trimester.

parenthood4

With my second, she was estimated around 5 and a half pounds at 36 weeks. She was born at 39 w 5 d weighing 7 lbs 7 oz. So if they estimate that they gain half a pound a week at the end, it was pretty accurate. But I've also heard so many stories about it being wrong!

mamaroar

They measured my little dude at 34 weeks and he was 5lbs 9oz, which my doctor called 68th percentile, and he was also 68th percentile for size at my 20 week anatomy scan.  That weight sounded "big" to me for 34 weeks but my doctor said it was completely fine.

However - I do see how the margin for error comes in.  They bascially take measurements and then try to calculate volume - and from U/S tech to the next, it seems to me that moving that cursor on the measurement even 1/4 centimeter one way or the other would produce a very different result. 

katy0990

I have not delivered yet, so I can't speak to the accuracy. But, I had a scan on Monday at 38 w 5 d and I was told there is a margin of error of 1 lb 4 oz. I am not sure if that margin applied to everyone, though.

Knottie1456889319

My growth scan at 36 + 5 said 6 lbs 10 oz. baby boy was delivered at 39+3 weighing 6lbs12oz. 
Clearly they were wrong.

They also told me he had short femurs which I had an anxiety attack over for 3 weeks and he was born at 21inches with very long legs.

What I mean is:  they have no idea what they are talking about. 

Zoyiaperry

My first was estimated in the 5 lb range and my doctor didn't think she would hit the 6 lb mark. She was born at 39 weeks and weighed 7 lb 12 oz. 

Sweet_D

I had been having u/s twice a week for 1.5 months because of suspected IUGR at two different doctors offices. 

36 weeks 4 days estimated to be 5 lbs 1 oz at regular dr appointment - on 37 weeks estimated to be 4 lbs 13 oz at high risk u/s. Born 37 week 1 day at 4 lbs 8 oz. so pretty accurate for me

mamaroar

@lanatalia - Today will be my last size for scan, and my doctor has warned me not to count on these numbers being correct.  She has expressed concern over women getting freaked out about having too big/too small babies when the margin of error is so big.  She says that these three scans in the 3rd tri are about progression and trajectory of his growth, not about determining what we think a birth weight will be.

But you guys know how this goes - when they do anything that assigns a value to your baby (heart rate, percentile, etc.) you feel like you have to go look it up and see how it compares to averages - no matter what they tell you!

oceanchild

anecdotal from two of my friends: 
when i was preg with #1 (est to be 9+ pounds, born at 8#4oz including fluids from L&D), she was preg with her #1 - they estimated her baby to be almost 12 pounds and told her she would have to have a c/s. her baby was 8#8oz at birth.
second friend was told baby was estimated to be just over 7# at birth, and her baby was born 2wk ago at just over 10#.
many people i know have guess weight vs birth weight differences, and some have been closer to accurate (just luck, IMHO), but those are the two with the hugest discrepancies that i know personally. 
my 2nd was less than her guess weight by a pound and a half. 
my new OB (with 3rd baby and this baby) says he "doesn't bother with that nonsense unless there is clearly something to be concerned about" so i haven't had guess weights with my last 2

mastib

There is a 10% (give and take) from the number they get from the US.
For small babies it is far less than it is for bigger babies. 
They were accurate with my last one and 
I expect this one to be pretty accurate as well. 
A friend one mine just had hers and they were exactly right. 

mille116

My growth scan showed my daughter to be 10.5 lbs at 40 weeks. They wanted to do a c-section. I fought them and wouldn't agree. My daughter was born at 10 days past her due date and was only 8.9 (I gave birth vaginally with no tear). I am not having a scan this time. God gave me this baby and by God I will birth it lol..... Or at least try haha

BrittaniLC

My u/s was right on the money. I had the scan on a Monday and they estimated 8lb 8oz. She came on the following Thursday weighing 8lbs 8oz! I was skeptical at first, but they were right!

FutureMrsCaesar

My ultrasound at 34 weeks predicted her to be 7lb 7oz and she was just born (yay!) at 7lb 3oz a week early. So it would have been pretty darn close. 

clairemwalker

I had a growth scan 3 days before i delivered. They estimated 3kg and she came out af 3kg110grams. So pretty close in my instance

goatgirlnyc

I'm a May mom but I saw your post on the homepage. 

I was overdue for my first who is now two and a half. The last month of my pregnancy, I had a weekly ultrasound because of my age ( over 35). They kept saying how huge the baby was. The technicians were telling me my son was over 10 pounds pushing 11. My ob encouraged an induction, etc., etc....

My son was just long and lean weighing in at 8.5 pounds. A good sized baby but ultimately they were off by a good two pounds.

kitteh81

A few days before my second was born they estimated her at 7 lbs 12 oz.  She was born at 40+6 at a solid 9 lbs 10 oz, and I didn't have gestational diabetes.  There's no way she gained almost 2 lbs in a few days!

Knottie59802221

I just asked my doctor for an estimate because of this thread and she refused to give one. She said no one could accurately guess but that my baby is a normal and healthy size. 

Stormiewinter

My growth scans were both pretty accurate. Ds1 36 weeks estimate 5lbs 4 oz born next day at 5 lbs 7 oz. Ds2 37 week estimate 6lbs 2 oz born 3 days later at 6 lbs 4 oz. 

LuckyCookie80

@Knottie59802221 I'm wondering if I'm in the same boat. I haven't had an ultrasound/scan since January and had one pelvic exam at about 36 weeks (when they told me I was zero dilation, baby was head down but still high). I assumed I'd be getting a pelvic at my weekly appts but the OB advised only if I requested them for my own curiosity otherwise there wouldn't be any ultrasounds or pelvic exams unless medically necessary and I was just waiting for LO's arrival at this time.  Reading about all these growth scans I'm wondering why my OB hasn't indicated I'll have one but sounds like some are getting the estimated weights at the hospital upon check-in.  What if LO is a weight that induction would be recommended...would the OB not even know without the scan?  I've had a pretty kosher pregnancy so maybe since I have no issues the OB doesn't feel it necessary to check? I have an appt tomorrow evening so I'll be asking about this growth scan. I'm also going to opt for a pelvic to see if LO is still head down (was previously breech), and if I'm dilated at all (own curiosity I suppose). DD 3/18

mamaimmoos

@LuckyCookie80, my DD is 3/14, my last ultrasound at 34+3 to check our fluid levels and that was it.  My Doc also doesn't do "growth scans" because they are unreliable.  We also did a pelvic exam that week (I was "about a finger tip" and baby was head down) and then I didn't have another pelvic until today at 39+2 (2 cm, 70% effaced).  I have had a very easy pregnancy and don't have regular contractions happening so she didn't find it necessary to check me weekly.  The only reason she checked me today is because I asked her to.  I think it is really a per doctor thing.  She does think he is going to be a big baby and my family has a history of chubby babies but it isn't causing her any concern in regards to how or when he arrives.  She is letting him make the schedule.  I will say it is nice to know that there is some progress happening since we are so close to our guess date.

Stormiewinter

@LuckyCookie80 my doctor doesn't normally do them, but I suddenly went from measuring 1 week ahead to measuring 2 weeks behind and she was concerned about the shift. Turns out baby had just dropped. 

sgregory25

I had my ultrasound at 36 weeks and she estimated him to weigh 7pound and 12 ounces. He was born today at 40+4 today at 7 pounds and 11 ounces. So it was almost spot on.