Does anyone know how accurate fetal weight measurements are? I am 28.5 weeks and my baby is measuring 1510 grams or 3 lbs 5 oz. At this rate I am going to give birth to a toddler!!! I am a little worried to say the least. This measurment was taken via ultrasound.

asked 24 Nov '09, 02:27

dreamerisme's gravatar image

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edited 24 Nov '09, 02:43

I have always heard that ultrasound estimates are not very accurate. This abstract seems to imply that there are quite a few different methods to arrive at an estimated weight with varying levels of accuracy. In 2006, the New Zealond Medical Journal published study covering one hospital and 1177 infants that concluded the following:

The accuracy of ultrasound estimations of fetal weight performed at Wellington Hospital within 7 days of delivery in term singleton pregnancies was at least similar and sometimes better than that reported in other studies. For one in four women, however, the fetal weight estimation was more than 10% different from the actual birth weight of their infant. Ultrasound measurements had a tendency to overestimate the weight of small infants while underestimating the weight of both large infants and the infants of diabetic mothers. As the reliability of ultrasound estimation of fetal weight to detect larger babies was poor, the use of such an objective measurement in the management of suspected macrosomia in term singleton pregnancies should be avoided.

answered 24 Nov '09, 03:41

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Kiesa ♦
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Anecdotally, I've never seen them to be particularly accurate - they are sometimes off as much as a couple pounds for the double-digit monsters. We never gave any credence to the estimate for our second child - and for some reason he had much more sophisticated imaging done (perhaps it was just the standard or the policy at that hospital 3 years after our first - she was imaged several times due to our multiple hurricane evacuations and no medical records etc).


answered 24 Nov '09, 03:33

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Cade Roux
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When i was 28 weeks they told me my baby was estimated to weigh 4.1 lbs, so in which we expected to have a mamoth child. At 31 weeks the growth rate kept up, and my Dr. decided to induce me at 36 weeks, because my baby measured 8.8 lbs. Yeah, well I gave birth to at 5lb 6 oz baby. Dont get me wrong he is very healthy and strong, but yes, they can be way off!!!! Good luck though!


answered 24 Nov '09, 13:01

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Becky 1
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I'm shocked that a doctor would choose to induce a preterm labour on the basis of an ultrasound estimate of weight. 8lb 8 oz isn't even that huge.

(24 Nov '09, 13:19) Meg Stephenson

Was the weight measured via ultrasound measurements or just by measuring your stomach?

I don't know any specific statistics on accuracy, but from my personal experience, 2 weeks before I had my twin boys, from an ultrasound they were estimating their weights to be over 6 pounds and they ended up weighing 5lbs 10oz and 5lbs 11oz. So they were not very accurate for me, however, my understanding is that the ultrasound measurements are more accurate than just your physical measurements, but still neither one is an exact science.


answered 24 Nov '09, 02:37

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Shannon B
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Thanks Shannon, I made an additional note that yes that weight was arrived at via ultrasound.

(24 Nov '09, 02:44) dreamerisme

Ultrasound exams are notoriously inaccurate for predicting the weight of your baby. The ultrasound gives an estimate of the weight of your baby, but this estimate can be off a pound or more in either direction.


answered 24 Nov '09, 20:15

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My son measured 8 lbs - born 2 days later at 7lbs. For my daughter, they said 8.5 lbs, which I thought strange because my dr. said that the baby didn't feel to be very big. Born 3 weeks after the ultrasound - only 6lbs! Way off! I think it depends on the tech. My third is due in 4 weeks, and they estimated 5lbs 15 oz right now. Seems reasonable, but who knows?


answered 13 Jan '11, 17:56

chasinamie's gravatar image

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I know from experience that they are not very accurate. My wife had a fetal weight measurement while she was in early labor; they estimated the baby to be about 8 lbs 3 oz. The baby was born less than 24 hours later at 9 lbs 8 oz. I would not put too much trust in fetal weight measurement.


answered 24 Nov '09, 15:42

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Matthew Jones
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My sister-in-law was told at 38 weeks that in the ultrasound her baby weighed over 10 lbs. She stressed for about two days whether she should be induced and then went into labor on her own. At birth her baby weighed just over 5 lbs. Don't get worked up about an ultrasound. My own baby was estimated to be 8 and came out 10 lbs. 3 oz. Doctors should explain the possible inaccuracies when they make the estimation.


answered 04 Oct '11, 08:20

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Asked: 24 Nov '09, 02:27

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Last updated: 04 Oct '11, 08:20