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Hello there...
I just went in for an ultrasound and I had thought I was 10w 3d based on my LMP...but the ultrasound measures the baby at 9w 4d.

Does anyone know how accurate the ultrasound measurments are? Could it just be a smaller baby than normal?

I'm one of those people who has to know EXACT dates for everything
Please share any experience you all have with this!
Thanks so much!

Sara
expecting our bundle of joy on 3/29/03
 

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LMP isn't really the most accurate way to determine due dates, unless you have a textbook cycle (always 28 days, with ovulation on day 14). MOST babies measure within a very specific range in the first few weeks, that's why ultrasounds can be used for dating. But when we had one of these "dating" ultrasounds, it was still given as +/- 4 or 5 days, can't remember which. So say your cycle was a little off of the textbook average, and your baby is slightly smaller than normal, you should easily be within the normal range. Sometimes doctors don't even change a due date, despite ultrasounds giving a different date...but if this is your first baby, I'd take every week I can get
Even if you don't go over at all, depending on what your practitioner situation is, some get antsy to have the baby before 40 weeks have even passed...so having an extra week on your side might be a good thing.

And...birthing is one of those things that you won't be able to get anywhere exact. I've read that only 5% of babies are actually born on their due dates (although a recent poll here seemed to have a higher percentage). It might be easier if it will stress you out to start thinking end of march/early april, rather than a specific date. Otherwise, if you have to watch your due date come and go, it can be hard (speaking from experience here...and my first baby was only 6 days "over" due, hehe).

Best of luck, march mama, and hope this helps!
 

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Agreeing with Jster's comments here. Yes, ultrasounds can vary widely depending upon the skill of the technician, equipment, time of day, full moon, etc. OK, that's a tiny bit exaggerated, but the measurements are taken based upon grainy images and are subject to the technician's discretion and skills. Due to the nature of taking these virtual measurements, results can vary widely. In addition to the subjective measurements, the calculations are based upon formulas in regard to *average* fetal growth. Some fetuses grow faster and bigger, some are slower and smaller. At the end of gestation, most are around the same weight (between 7-9 lbs) but the growth rates to get there may have been markedly different. The EDD of an ultrasound means virtually nothing in regards to your true due date, and that is subject to when your baby is ready to make an appearance too.


I had an ultrasound done during the 37th week of my last pregnancy and the EDD had me delivering that day (ha!) and a 9 lb, 13 oz baby at that. I didn't deliver until my "true" EDD of Sept 6th and that was only due to complications and a cesarean delivery. DD was 10 lbs, 6 oz, BTW.

Don't stress about the ultrasound measurements and your EDD as the reading you get from one technician can be quite different than those from another. HTH!
 

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My dr said ultrasound measurements are accurate +- 1week. My cycle length is 35 days, so my LMP calculation is not that accurate. With my first ultrasound at 6 weeks, I was 6w5d. Two weeks later (same day of week), I was 9w2d. Somehow it was already off by 4 days. With my LMP calculation, I would have been 9w5d. As Jster said, its really only a guide. The baby would come when its ready.
 

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I 100% agree with Jster. I was under treatment of an RE and knew EXACTLY what day I ovulated (it was triggered) and my u/s was off by a couple of days at 7w. The tech told me their dating was +/- 4 days. Think of it, that little baby is soooo small a teeny bit one way or the other with the measurement throws the dates a bit off.

But the biggest thing is that if you're dating from LMP and not O, LMP assumes you ovulated 14 days later. If that was not the case, then those dates will be off.

Also, the time until implantation is not consistent so dates can be a little off from that as well.

Full term is 37-42 weeks. I cannot get over that OB's still give a single day as an EDD! My SIL's EDD was exactly one week before mine and she is now holding her baby boy born at 32.5 weeks! Now, that is not very common, but still, counting on babe to arrive on ONE specific day of those 5 weeks is a lot to ask for!

Get ready now for all sorts of things not to go as planned... babies don't work that way
 

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I generally agree w/all of the above...

My son AJ was "due" 9/17, his ultrasound predicted 9/25, my cycle is 33++ days, i knew the day that i conceived (12/25)...
At 36 weeks we had an ultrasound, predicted that he was 5lbs 10oz. He was born at 38 1/2 weeks and was 6lbs 1/2 oz. on (9/9)

I don't know if anyone really knows anything!!!!!!!!!!!
 

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Congrats on the pg! :)

I had an u/s done at 8 weeks to date the pregnancy since I'm irregular. One u/s photo said 7w4days and the other one said 7w6days. So it depended on the angle they were measuring at. It was sooo tiny at that point, they said as long as it's in the general ballpark I was keeping my same due date based on LMP.

Darshani
 

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I actually had a due date u/s at 9 weeks 2 days in this pregnancy, which was totally unnecessary considering I knew the conception date (I already have 2 kids, one co-sleeping, so there isn't a lot of question around here about conception date if YKWIM). Anywho, my OB did it himself and it dated me exactly at 9 weeks 2 days (I said, "told you so"). He said they are more accurate to date early(like more accurate than the 20 week u/s is), that's why he does them routinely. Also, they normally won't change your due date unless you are more than 3 weeks off.

I think the main reason they like to know your due date is so that they can do the AFP at the right time (which I wouldn't do anyway), but also so that when you are at 41 weeks or so they can start pressuring you to induce or section, but that's my NSHO.
 
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