ultrasound and weight guestimates

[livinzoo]

I had my anatomy screen at 19 weeks and 1 day. They said she weighs 11 ounces. Everything I read says the fetus should weigh that around 20-21 weeks. Is this normal? I have to have another ultrasound at 28 weeks in hopes that my partial previa rises up.

[gemasita]

The inaccuracy of ultrasound

First trimester: 7 days
14 - 20 weeks: 10 days
21 - 30 weeks: 14 days
31 - 42 weeks: 21 days

[lillymonster]

Originally Posted by livinzoo

I have to have another ultrasound at 28 weeks in hopes that my partial previa rises up.

I personally don't understand them doing one for that reason at 28 weeks, I would put that off, it's not going to move by that much around then and they can't do anything about it except give more time to threaten you with a c-section. Mine showed up at 20 weeks and no u/s again until like 36 weeks and by then I was in the clear. It will move or it won't by then, and at that time they can make the decision.

[MaerynPearl]

Originally Posted by lillymonster

I personally don't understand them doing one for that reason at 28 weeks, I would put that off, it's not going to move by that much around then and they can't do anything about it except give more time to threaten you with a c-section. Mine showed up at 20 weeks and no u/s again until like 36 weeks and by then I was in the clear. It will move or it won't by then, and at that time they can make the decision.

I was diagnosed with partial previa at 21 weeks and by 27 mine was totally clear of the OS.

If it hadnt moved, i would have had to have another us a month later.

[MyFullHouse]

Originally Posted by livinzoo

I had my anatomy screen at 19 weeks and 1 day. They said she weighs 11 ounces. Everything I read says the fetus should weigh that around 20-21 weeks. Is this normal? I have to have another ultrasound at 28 weeks in hopes that my partial previa rises up.

Your fetus obviously hasn't read the books!
If they all grew uniformly, we wouldn't see both 6lb and 10lb full-term babies, now would we?

FWIW, my u/s at 19w2d measured 11oz. That doesn't mean my baby actually WAS 11oz, but it's an acceptable rough estimate. I'm not about to have him taken out and put on a real scale to be sure!

[aikigypsy]

Ultrasound weight estimates are notoriously unreliable. They thought that my DD (post-dates at 42+ weeks) was going to be 10 pounds -- 8 lb. 11 oz. and pumped full of fluid at birth.

As for the previa, I've spent the last month reading about it non-stop, and I don't know what to believe any more. At 20-ish weeks, about 5% of women have it. At term it's down to .5% or less, depending on what study you look at. The trouble is, I don't think anyone has gotten enough data together and properly analyzed how many births at, say, 30 weeks have previa vs. births at 40 weeks, and it will be harder and harder to get those numbers as obstetricians push for earlier and earlier c-sections. The basic fact is that the bigger the uterus gets, relative to the size of the placenta, the less chance there is that the placenta will cover the os, except in those cases where the placenta is centered over the os.

I have now heard/read of several cases of the placenta "moving" dramatically at around 36 weeks, a time when many OBs would be pulling out the scalpel for a section, to guard against the chance of the woman going into labor, and often without a last double-check of the placenta's position.

[Mommie020307]

I have an ultrasound scheduled for Friday(8/13) I will be 33w6d. Reason for the ultrasound is cause i am losing weight and measuring 3-4 weeks ahead. My due date is Sept 25th. So i am hoping that they bump my Due Date to EARLIER than 9/25

[Adamsmama]

My baby has measured 3-4 weeks ahead by weight on the u/s we have had (18 weeks and 22 weeks) ... I'm sure I'm growing a larger than normal baby seeing as mine have all been between 8-10 pounds at full-term which is larger than the average.

[mom2threenurslings]

The four measurements that are taken with an ultrasound for weight ESTIMATE are the baby's head circumference, the biparietal (sideways across the baby's head) diameter, the abdominal circumference and the length of the baby's femur (thigh bone). The u/s tech then uses equations to "convert" these measurements into a weight estimate, which, depending on how many weeks along you are, can be off as much as a pound or three. And every baby is different, so if your baby has longer legs than the average baby, your baby could measure as weighing more just because of that.

My personal experience - when I was pregnant with my first, I was told my baby was 10.5 lbs via ultrasound ... I was induced and he was 7lbs 2oz at birth.

In my experience, my big babies were much easier to birth than my small babies ... my easiest was my biggest at 10lbs 14oz (homebirth ... my body pushed him out in 7 minutes).

[mama to 2 girls]

Like everyone else has said, u/s can be really off.....But with that being said if I went by my 19-20 week u/s's with all my kiddos they have been pretty much right... With dd1 and dd2 they measured right on at 19-20 weeks and they were both 8lbs. give or take a couple of ounces. With my ds he was "weighing in" at 12 oz. at 19 weeks and he was a 10lber. He was by far my hardest birth but he had a huge noggin....my favorite saying is that fat squishes!

[cinderella08]

They can be way off, an they can also be nearly dead on.


I had an u/s to make sure my placenta moved up at 37 weeks. Baby girl was estimated 8lbs 15oz. She was born exactly one week later, 38 weeks on the dot at 6lbs 13oz - TWO pounds less than estimated.

My ultrasound today - at 38 weeks - yielded a 6lb 6oz baby boy. Totally believable since my daughter was born at exactly this time just a few ounces larger.