The accuracy of ultrasounds?

[spookymama]

I know the later in pregnancy ultrasounds are done, the less accurate they tend to be. I know this tends to hold true for weight, being more than a pound off in either direction. Does this apply to measurement as well?



My dates are right on, but according to the doctor yesterday.. the baby was only measuring at 38 weeks, and I am 40.

I'd love to hear your thoughts on this, or any experiences you may have had!

[Jane]

Are they trying to attach meaning to that? To me, that's just trivia. If the lab uses a 7 pound 12 ounce baby, at 21", as the 40 week "standard", then you are on target to have a 6.5 pound baby at 19.5" long if you birthed today.
If you'd been measuring ahead and then fell behind, or the fluid levels decreased or the uterine artery flow was bad, then I would worry that baby was being growth restricted.
Just that information by itself - trivia.

[melbatoast]

Yeah, that.

[spookymama]

Originally Posted by Apricot

Are they trying to attach meaning to that? To me, that's just trivia. If the lab uses a 7 pound 12 ounce baby, at 21", as the 40 week "standard", then you are on target to have a 6.5 pound baby at 19.5" long if you birthed today.
If you'd been measuring ahead and then fell behind, or the fluid levels decreased or the uterine artery flow was bad, then I would worry that baby was being growth restricted.
Just that information by itself - trivia.

I'd be measuring on target for an april 6th due date, for the two ultrasounds that I've had. But according to him I am two weeks behind, I am 38 weeks. He was pretty insistent on getting my other ultrasound records, as he did not believe that I was at 40 weeks. There isn't anyway I can't be at 40 weeks.

He didn't mention growth being restricted (surprise of surprise). I was just curious about measuring behind now and what the accuracy of that is. I think I read somewhere that it can be off by 17 days?

[~Megan~]

Not a professional, but the weight estimates are based on the measurements. If weight can be off so can measurements.

I think you are probably just having a small baby I'd not worry about it at all.

[Jane]

The rule of thumb I use is 10% of days. So, at 6 weeks, it's +/- 4 days (10% of 42), at 20 weeks, it's 14 days, at 40 weeks the formula starts to slip...it's more like your 17 days, yes.

Did you go early or late with baby #1 (and how big was lil' chaos)? Usually, moving the due date back is a non-issue, because it gives you more time to go into labor spontaneously and naturally. And, since you're "38" you are not pre-term either.
If your dates are correct (and I believe you!), there is a huge chance you'll go into spontaneous labor in the next two weeks.

[spookymama]

Originally Posted by Apricot

The rule of thumb I use is 10% of days. So, at 6 weeks, it's +/- 4 days (10% of 42), at 20 weeks, it's 14 days, at 40 weeks the formula starts to slip...it's more like your 17 days, yes.

Did you go early or late with baby #1 (and how big was lil' chaos)? Usually, moving the due date back is a non-issue, because it gives you more time to go into labor spontaneously and naturally. And, since you're "38" you are not pre-term either.
If your dates are correct (and I believe you!), there is a huge chance you'll go into spontaneous labor in the next two weeks.

I went late. 3 days over my due date. Technically I am 5 days over by ovulation, or 1 day over by LMP.


Thank you so much for answering my question!