Inaccuracy of 3rd trimester ultrasound measurements / IUGR?

[ariane77]

I'll be 37 weeks tomorrow, and so far we'd declined all ultrasounds.  Since we were planning a homebirth, we went in for what was supposed to be one quick ultrasound to check the position of the placenta yesterday.  The perinatologist recommended by our midwife ended up doing measurements of the head, abdomen and femur, and told us that the abdomen and femur were measuring several weeks behind the head - so he's concerned about asymmetrical intrauterine growth restriction.  Everything else he checked (amniotic fluid, blood flow through the cord, development of heart, bladder, etc) were normal.  He wants us doing nonstress tests every three days and come in for another u/s in 2 weeks - if the baby hasn't grown, he (and the midwife) will want to induce.

We passed the first nonstress test last night.

The perinatologist was really confusing in interpreting the results. He kept pointing out that neither my husband nor I are big (and we also moved to semi-high altitude during the pregnancy) so "perhaps it's just a small baby". However, *every* time he said that, he followed it up with "but the measurements shouldn't be so asymmetric".  Not really sure what to do with that.

Anyway, I'm freaking out, and I guess looking for some information about whether 3rd trimester u/s length measurements are known to be as inaccurate as u/s weight estimates. Isn't the weight estimate based on the length measurements somehow?

Did anyone have similar measurements in the 3rd trimester?

[Plummeting]

That would worry me, and I generally tend not to worry about stuff like that. We had our own issues with being told our baby was "too small", but it was different and we opted not to go back for repeat ultrasounds. (I missed their cut-off by one day, I knew I had conceived later than they thought, the baby was symmetric, other than having a slightly chubby tummy, which is not indicative of IUGR, etc.) However, being several weeks behind in the limbs, with a large head, would definitely concern me. A small baby shouldn't be so asymmetric in that way, even if you did move to a higher elevation. I haven't been through what you've been through, but I did have a situation surrounding size of the baby and had to spend a few weeks learning as much about IUGR as I could. I would not be comfortable simply hoping for the best with the large head/smaller body combination.

[Bokonon]

When the head measures greatly ahead of the abdomen, it is a concerning sign.  I believe it's called brain sparing, where the fetus' head grows and the rest of the body lags behind, when there is insufficient bloodflow or oxygen to grow the body evenly, because the brain is most important.

It sounds like the peri. is being cautious but not alarmist.  I think planning for induction at 39 weeks for suspected IUGR and asymmetrical growth sounds reasonable.  I'm not a medical professional, but my babies had IUGR due to preeclampsia.  Neither had brain sparing, but it was something that was looked for at every ultrasound because it was a possibility.

[fruitfulmomma]

We were told something similar with our 3rd at an ultrasound to check on her because we were considerably passed edd. Her limbs were measuring really small with possible enlarged heart.

I opted to go ahead and induce by arom and have her at the hospital since there was really no way of knowing for sure. When she was born she had some problems breathing, I think delay in cord cuttung probably would have helped, but the pedi team rushed her to nicu and got her stable and she only needed room air. They ran all their tests and everything was normal except she did have a slightly enlarged heart but ped did not think it was an issue.

She probably would have been fine at home but with what info I had I still believe that her birth was best in the hospital.

[katt]

is there anyway you can see a different Peri, at a different location, and get a second opinion?

[ariane77]

Thanks everyone for your thoughts.  We got a second opinion last week, as Katt suggested, and this perinatologist told us everything looked fine and was measuring within a week of each other.  ???  Also put the estimated birth weight at a full pound heavier than the first guy.  So we basically have no idea what to believe, but are cleared for our homebirth if we want it.  I'm trying to be cautiously optimistic.  I suppose this is what I get for getting an u/s after reading about how inaccurate they are for the last 9 months.
 

[AmiMom]

Off the top of my head, I know that measurements can be inaccurate in late pregnancy... but that's more for guessing size, I don't know if it would be inaccurate from head to femur measurements. Late pregnancy ultrasound is better for checking fluid levels, not growth in my understanding. Good luck!

[Ellismom]

I know it's certainly possible for those measurements to be off. I have a close friend who wanted a natural hospital birth, but a late ultrasound showed abnormal growth. They induced out of concern for the baby which led to an epidural which (arguably) led to an emergency C-Section. Of course, sometimes concerns that come up with late ultrasounds are founded, but, in her case, her baby was born in perfect health with absolutely normal measurements. These decisions are so tough!

But it's great that you had the opportunity for a second opinion.