Sonogram accuracy

[Anonymous]

So, I just got back from my 36-week sono and my DS is purportedly 7.5lbs already. He's measuring in the 96th percentile and will likely be about 9.5lbs when he's born. How accurate is this info?? Anyone have stories of their sono measurements being dead-on or way off? I've discussed inducing at 39 weeks with my doctor, but I wanted to get some accounts of how accurate these measurements are before we decide. Thanks!

[Anonymous]

I had a sonogram at 37 weeks and they predicted 10 lbs. My daughter was 9.15 at birth (almost 40 weeks). Hope that helps with your decision. I think there is some + or - on these measurements though.

[Anonymous]

My OB admitted that these measurements have a 25% margin of error.

On the side of anecdote, I have always heard of them being in error in terms of estimating too large. Many, many, many women discuss being induced or talked in to scheduled C-sections due to fears about babies being "too large" only to have normal weight babies emerge.

My personal experience was that - based on sonogram - they estimated that my db would be over 10 lbs and db was only 8 lbs 9 oz (still large, but a far cry from 10 lbs). I have a close friend whose db was estimated to be over 9 lbs and was 6 lbs plus.

I would make NO decisions about induction based on estimated fetal weight. In addition, there is research that indicates that - in the cases where a fetus is truly large (over 9 lbs) - that induction is far riskier than vaginal delivery and frequently leads to C-sections. I'm sorry that I don't have citations for you - the research I did on this was several years ago before the birth of our db, but I found all of it online.

Decisions about induction should be based solely on medical issues like deteriorations of the uterine environment and other factors.

Best wishes to you and your db!

[Anonymous]

Keep in mind that the size that affects vaginal birth is mostly head size, not total weight. So if your baby has packed on the fat but has a normal head size, what's the problem? Conversely, if the baby's head is huge but hasn't but on enough fat, labor could still be tough.

[Anonymous]

I've heard of so many women whose babies were estimated to be much larger than they were; but I've never heard the reverse. My baby was predicted to be quite large (I can't remember how big) but only ended up being 8 pounds 6 ounces. Big, but not huge. And the weight babies put on towards the end is just fat, which isn't what makes labor difficult. I would not consider inducing based on size estimates.

[Anonymous]

I'd heard that sonograms tend to overestimate size, but my case was the opposite. My last sonogram predicted DD was 8 1/2 pounds or so. My doctor felt my tummy and said that she feels more like a 9 pounder. She was born a few ounces shy of ten pounds.

I would not bother with induction. My doc advised me that babies get fatter during the last few weeks in utero but the head size and bone structure in general aren't getting any bigger at that time. And that's the part that hurts on the way out. As the mother of a bigger newborn, I can say there are some advantages. They more they weigh, the better they can maintain their body temperature, so they have one less thing to fuss about. And I hear the bigger newborns tend to sleep better and that's been my experience, too.

New reasearch is pointing to problems with infants even a few weeks premature:

http://www.nytimes.com/2008/05/28/health/research/28birth.html

[Anonymous]

Ditto what the others said about babies being smaller than the ultrasound. In my case, though, it WAS accurate and my baby was over 9 pounds. My dr. didn't think I'd have a big baby since my fundal (?) measurement was always small. She was large, but my delivery was fairly easy. So I guess my advice would be to ignore the measurements if they are stressing you out. Size of the baby is not necessarily indicative of the type of labor and delivery you will have.

[Anonymous]

I must be an outlier. I had a sonogram for measuring small (4lbs 11oz at 35 weeks) and she came a few weeks later close to 7 pounds. There were predicting low sixes at best.

[Anonymous]

I had an ultrasound at around 35 weeks and the estimated size at the time was a little over 6 pounds. When I went into labor at 40+ weeks, my OB was fully expecting the baby to be over 8 pounds. Her weight at birth - 6 pounds 14 ounces. I have heard that the ultrasound can be off as much as 2 pounds (in either direction).

If you do end up going for an induction, you should know that your chance of success will depend greatly on how favorable your cervix is, especially if you are a FTM. Google "bishop's score". Also, pitocin can cause the baby to be malpositioned, and good position is key. My daughter's head was malpositioned and she essentially got stuck, I ended up with a c-section after 2 hours of pushing for failure to descend.

Good luck.

[Anonymous]

My first child went almost two weeks past due. I am a small person, and my doctor was freaking out - the sonogram showed she was going to be over 8 or 9 lbs. She came out at about 6.25 lbs. She was longer than average, and I think that might have caused the measurement issue.

My second child was born early but they also thought he was going to be large. I doubted it, and he indeed came out almost exactly the same weight as his sister had been.

I wouldn't induce due to predicted size - your body is made to handle the babies you grow.

[Anonymous]

A friend of mine was told 8.5lbs and that the measurements could be + or - 1lb. She delivered a 9 lb baby the next week.

[Anonymous]

I don't remember the timing, but perhaps at 32 weeks, I had a sono and the doctor said it was a big baby and I "might have to have a C-section." I freaked out a little and did a lot of research, and found that the biggest predictor of C-sections for size is the OB's *perception* of size rather than the actual size. So you have a lot of big babies delivered perfectly healthy vaginally, and smaller-than-expected babies delivered by C-section. I had another ultrasound several weeks later and the sono tech predicted he'd be ~8 lbs. at birth, and he turned out to be 7 lbs. 12 oz. (delivered vaginally). I felt like I would have been almost better off not having the sono at all.

[Anonymous]

Anonymous wrote: I felt like I would have been almost better off not having the sono at all.

I felt this way too. I am sure there are times when - through monitoring - different situations are able to be caught and addressed prior to labor. But, overall, I felt as though I wish I had not consented to or participating in the late term fetal monitoring and assessment. All it did was create a great deal of unnecessary anxiety and fear.

[Anonymous]

I totally agree with the above poster--all it does is make you freak out (usually needlessly).