Wrong Due Date on Dating Ultrasound?

snarkylibrarian · May 2014

So I finally had my first ultrasound and was super excited and relieved to see a happy, active little baby wriggling around. But then they told me that I was measuring at 10 weeks and 1 day, when I'm supposed to be 11 weeks and 3 days. That really seems impossible to me, because I've been charting like a mad woman for months before conceiving, I took ovulation tests and according to my last menstrual period, my conception date was on March 3rd. I had a positive ovulation test on the 3rd and had sex on the 1st, 3rd and 5th (temp surge post ovulation happened on the 4th). I didn't have sex for over 2 1/2 weeks after that. So I can't see how I'm THAT far off from my original due date. A few days maybe, but over a week? Just not possible. I told this to the woman giving me the ultrasound and she said, "It's not an exact science". But now they are changing my due date based on this ultrasound that I swear is wrong.

Has this happened to any of you? I'm kind of frustrated by it, because I love reading up on development week by week and am waiting anxiously for the 20 week scan and now it's over a week pushed back. And if you were convinced it was wrong, what did you tell people your due date was?

Acedit · May 2014

I personally do not have experience with this, but have had friends who have. The baby measured behind in the begining and slowly but surely grew and caught up to their original due date. Try to remain positive.... some babies are late implanters and can cause later due dates. Congrats on youre pregnancy... enjoy the next months ahead.

TC0514 · May 2014

I believe mine is off by at least 5 days based on reasons you mentioned. However, my last sono baby was measuring ahead (which would make my dates accurate) but my OB said she didn't want to change my due date yet. I have my NT scan today and if baby is still measuring ahead I'm going to ask again about EDD. Her calculations are 11/11/14 mine are 11/5/14.

turtles7 · May 2014

I charted as well and was measuring a week behind at my first ultrasound. I used the date the doctor estimated because it's just that, an estimate. Actually he kept switching back and forth between two dates so I just chose one. At my last appointment, baby measured a few days ahead of the due date. I know it sucks because now you have to wait a week longer for your next appointment. Could you try to reschedule to the week you want?

NunyaBennis · May 2014

Don't fret. I measured three days behind, then two days ahead two weeks later. Not enough to change my due date, obviously, but just reiterating that it's not exact. Honestly, I wouldn't mind having the EDD changed to a week later - potentially less pressure for induction & fewer texts/calls asking if s/he's here yet!
As for your 20wk a/s... it doesn't have to be at exactly 20wks. Schedule it a week or two before their mid-point date, that should be fine. They may adjust your "estimated" due date again at that time.
It sucks when you know you're right and are disregarded, but in this case just try to go with it. Not worth the battle.

MrsDL · May 2014

I know they say early "dating" ultrasounds are more accurate, but they are more designed for people who really don't have an idea of when they may have conceived - there is still a plus/minus of a week and the growth can change rapidly from ultrasound to ultrasound.

With my son (I charted so I knew) his due date based on LMP (which was about accurate) was 5/17. At the first dating scan at about 6 weeks they said 5/10. Then at the NT his growth indicated 5/7. The next one was 5/5 based on growth (had a lot of ultrasounds due to AMA). Well he was a large baby at 9 lbs 21.5 inches but he didn't show-up until 5/23 anyways - well after the LMP "due date."

With this one, we were measuring a week a head at the first scan at 7 weeks. Then 3 days ahead at a subsequent scan in my dr's office. At the NT yesterday, he was measuring 1 day ahead of his due date. My neighbor's daughter was measuring 3 weeks behind at one point with no growth for 3 weeks. She was terrified. Her DD showed-up perfectly healthy in the end 10 days before her due date.

Only about 5% of babies come on their actual due date (or somewhere around there) and they can grow ahead and slow down, or be behind and catch-up, or be ahead/behind a little the whole time and still come earlier or later than the due date. I'd just go by your first due date if you were charting and expect the LO to show up within a few weeks of that date. If growth is worrisome, your doctor would let you know. Really that's the most important thing. Having to wait for the anatomy scan is frustrating, but it can be done within a range, the dating doesn't impact the results like the NT scan which has to be done by a certain point. Your LMP will still be in your chart. A good doctor isn't typically going to rush to induce just based on dates, they look at the baby to monitor what's going on and to see if it's necessary. By your next scan, baby very well may be measuring at or ahead of what you think your due date is.

pennyandandy · May 2014

This happened to me with DS and is happening again this time around. My dr. has an ultrasound machine in office, but it's not the highest quality, and he is a general practitioner, so he is not an ultrasound expert. He usually takes the beginning measurements with the caveat that they are not 100% perfect. My dating u/s this LO was measuring a week or so behind. When I have my a/s they will send me to the hospital and have the tech do it so it is accurate. I'm not worried, the same thing happened with DS. He was wiggly and they couldn't get a good leg measurement on him until about 32 weeks or so.

lil_shocker · May 2014

You also need to take into consideration that your body is not truly pregnant until implantation, and when implantation occurs varies for everyone. So, you may have ovulated and fertilized the egg on march 3 or 4 or 5, but you could have had a longer period for implantation.

Really, it isn't a big concern that it was moved a week behind, especially since full term is considered 38-42 weeks. If you are worried about them indicing you too soon if you go past your due date, then let your practitioner know that you want to wait a little longer before inducing.

Maelara · May 2014

Your baby was moving with a good heart beat. Don't sweat the small stuff. You coul have implanted late. Plus, ultrasounds can be up to 5 days off.

brooklyngirl18 · May 2014

same here. during my dating ultrasound the dr put me 9 days further back than i thought but everytime i go in she says the baby is measuring a little ahead so i'm thinking my actual due date is somewhere in the middle. i agree with PP as long as everything looks good the due date isn't that important, just a guess.

ZAFrisbie · May 2014

I had my first ultrasound today and they placed me at a week ahead to what I think I am, based on charting. So, I think it's definitely an imperfect science and will change as the baby continues to develop.

ExcitedKJ · May 2014

My baby is measuring different than the dating U/S and my doctor told me that around a week they really don't worry about the dates and not to be concerned and in all likelihood they will probably see the baby measuring back to the original EDD next time.

Don't stress, it's probably nothing.

As to hopefully comfort you and show how incorrect U/S measurements CAN be, my closest friend was told in the last month of pregnancy (each week she had a scan saying the same) that her baby was very small and to the point it may not make it. The baby popped out at almost 7 pounds and perfect in January '14.

KitKat099 · May 2014

That is worrisome but at this point I think that as long as there is a baby and a good heartbeat you are probably fine. (At least that is what I am telling myself!)

Romiaaron · May 2014

From what I understand the egg can take up to 9 days to attach to the uterus once conception takes place, I'm not an expert but that may be the reason why the measurement is behind. Was your doctor concerned?

tguichon · May 2014

I had this happen too. Based on my LMP, I would've been 8 weeks 1 day. But in an emergency ultrasound that was done because of a blood clot. It said 7 weeks 2 days. The odd thing about that for me was I was on holidays then by myself and had a positive test (one that said 1-2 weeks pregnant) 2 days after what the us said my conception date would've been. And then 5 days after that had another positive test saying pregnant 2-3 weeks. Which makes my date make sense. I was hoping my doctor would send me for another ultrasound as this one was an emergency one and I never got to see it. But he wouldn't send me for one until the 18-20 week one. I booked that one and the us tech asked me how my NT scan was. I never had one and she said it was too late now!!!! So I won't Ben get to see anythig at all until 19 weeks. I even explained my missed miscarriage that was discovered on my last pregnancy at the ultrasound and so I really wanted one. But my doctor wouldn't send me for one. Kinda disappointed. And didn't even realize or know about the NT scan one.

snarkylibrarian · May 2014

Thanks everyone for the comforting reassurance. I am counting my blessings and am happy for a healthy baby. My midwife says not to worry, so I am not gonna stress it. It is just hard to know what to tell people for my due date. We are going to reveal to everyone on Mother's Day. I am just going to go with my gut and my charting and announce the earlier date.

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