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Discrepency in Ultrasound dates at 7 weeks pregnant
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Discrepency in Ultrasound dates at 7 weeks pregnant

Hi there,

I am currently about 8 weeks, 3 days pregnant.  Early in my pregnancy I started to spot very lightly, brownish, no cramps at all.  I went into emergency and they did a pelvic (my cervix was closed), checked my hcgs (they have been doubling and even tripling as they should) and an ultrasound.  This was at app. 6 weeks pregnant.  The vaginal ultrasound showed only a sac at this point, nothing at all on the abdominal ultrasound, and they said I was earlier than I thought.  11 days later I had a follow up ultrasound and this time on the abdominal they got a sac, and on the vaginal they got a sac, yolk and the beginning of a fetal pole, no heartbeat yet.  They dated me at 5.5 weeks even though my dates showed 7 weeks 3 days at this point.  The concern is that I am absolutely sure of my LMP dates as I was charting.  Also, we used an ovulation kit so I know I ovulated about 14-15 days after start of LMP.  So gestational age absolutely should have been 7 weeks, 3 days.  Actual age since conception should have been about 5 weeks + .  My Dr. doesn't seem overly concerned as my HCG's have been rising, I still have my pregnancy symptoms, the spotting has completely stopped (after 3 weeks), and there still has never been any cramps or any other signs of miscarriage. The tech, dr. and nurse all just keep saying my dates must be off, but I know they aren't.  At least not by more than a day or two. ( I tend to have 6 and 7 day menstrual periods)  I wouldn't even be remotely concerned if it wasn't for the discrepencies in these dates.  My Dr. has me coming in in 2 weeks for another ultrasound, but the wait is killing me.  I am wondering what other reasons there could be for such a difference in dates between LMP and ultrasound?

Thank you so much.
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242596_tn?1192429549
Hello,

It is not uncommon for pregnancy dating by ultrasound (U/S) to differ from dating determined by the last menstrual period (LMP).  The earlier the u/s the more accurate it is in determining the age of the pregnancy.  U/S is often used to confirm a woman's dating and if there is a discrepancy, the u/s dating is used.  General guidelines are that if a 1st trimester u/s differs 7 days or more, or a 2nd trimester u/s differs 14 days or more from the due date based on the LMP, the u/s dating is used.  If the due date is within the 7 or 14 day window the LMP is used

Also, if a woman is not certain about her LMP it is usually best to use u/s dating.

Despite the certainty of your dating, given how early the u/s was I'd use your 5.5 wk u/s date to calculate your due date.  

Why the difference?  I don't know, usually it is a result of an uncertain LMP or delayed or early ovulation.  Nonetheless, you have a healthy, normal early pregnancy.

Congratulations!

Dr. Downing
9 Comments
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377493_tn?1356505749
I just wanted to thank you for responding.  Although the difference in dating still really doesn't make sense to me, you helped put my mind at ease.    You basically told me the same thing my dr. did, and hearing it twice made a big difference.  I am glad there is a site like this as hearing it from a Dr. is a far cry from hearing from a chat forum.

Thank you again.
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Avatar_f_tn
My u/s showed a sac that was 5 weeks 3 days. The LMP measures that I should be 7-8 weeks, but I am irregular.  My MD scheduled me to come back in a week to check viability.  He already stated that if we "don't see anything" that he would want to schedule a DNC.  Coul dthe u/s be right and the calculations off?  Is he just saying this to not get me excited?  Or is there really a problem? What are my chances of a normal pregnancy?  I am healthy and this would be my first time being pregnant.  Help :(

Thanks!!!!
Suzie
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Avatar_n_tn
I have an issue/question with your advice to adgal.  Last Friday I went to an ultrasound, was supposed to be 13 weeks, but found out I had miscarried and the baby measured 9 weeks. Now, I'd had 2 other ultrasounds, one at 8 wks and 10 wks (by my calculations).  At the one at 8 wks, everything seemed normal, but when I went to the doctor at my 10 wk appointment, she told me the previous u/s put me at an Aug. 7 due date rather than the July 31 one I had calculated by my period.  I was confused like adgal, but like you, the doctor said it seemed fine, and my ultrasound that very day showed that the baby measured 8 wks 5 days.  The tech said the heartbeat was strong and the baby had grown so not to worry, like your advice.  Last Friday, when I was in the u/s room and learned I'd had a missed miscarriage, the doctor (a different doctor; I was at a different prenatal clinic for an integrated screening) told me that my previous u/s's were signs - the fact the baby measured so small was a warning sign that it wasn't developing properly, especially since I had a strong feeling I'd ovulated at the date I'd first calculated (the July 31 due date) and hadn't even had sex the week the u/s put my baby at.  So I don't want to be alarmist for anyone, but instead of lulling yourself into a false sense of security, like me, only to be devasted thinking you were going into your second trimester, I'd advise having another ultrasound sooner rather than later to confirm that everything is going okay.  I'm not a doctor, but that is my thought.  

Since then, I've been riddled with anxiety.  I had a D&C on Tuesday. How long does it take those hormones to subside? I hadn't bled at all before the D&C. Could those hormones be causing part of this anxiety? I'm going to wait a few months before trying again, but I'm just so scared of a repeat of what's just happened.  

Thanks.
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Avatar_f_tn
I am curious to know what happened with your pregnancy, adgal.  When I read your question today, it was as if I had written it myself.  I had an u/s today, thought I was 7 weeks, 5 days.  The u/s today said I was 5 weeks, 6 days.  Two weeks ago I had an u/s and they said it looked like 5 weeks.  I also did an ovulation test and know that according to my calendar, I should be at 7 weeks, 5 days.  I am supposed to go back for another u/s in 2 weeks.  I am trying not to worry, because there's nothing I can do about it and I want to keep a positive attitude.
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Avatar_f_tn
I am so glad you brought up this issue.  I had a similar situation with my 3 pregnancies (all ending in miscarriage).  Because I was dating at least a week behind each time and knew for sure my LMP and ovulation dates, my doctors were concerned.  This time I had u/s at 7 weeks, but said dating 6 but with an OK heartbeat.  At 8 week u/s, embryo had only grown a few days more plus heartbeat was way low signaling inevitable demise.  Other than these indicators, I had no signs of miscarriage.  

Dr. Downing is providing the appropriate response when it comes to dating in general (i.e., dates can be off if you are unsure of LMP), but since adgal's description says she knows for sure, I'm not sure how being almost 2 weeks off doesn't seem to concern him.

Adgal, please let us know what happened (if you are still reading these of course).
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377493_tn?1356505749
HI all,

Unfortunately in my case my pregnancy ended in miscarriage at 9 weeks.  The reason they had so much trouble diagnosing it was that my cervix never opened and I never bled anything more than the brown spotting.  It was ultimately the ultrasounds, then my HCG's beginning to drop that told us what was happening.  However, please don't worry if you are also measuring behind.  I did a tonne of research during the waiting period between ultrasounds, and it sounds like it happens often, with still a positive outcome.  In my case there was never a heartbeat, and it seems the fetus had stopped developing at about 6 1/2 weeks.  They did analyze the tissue, and can't find any reason for it, so just "one of those things".

I wish all of you the best of luck.  I wasn't sure if I should tell you what my outcome was, as I didn't want to worry those of you experiencing a similar situation.  Your case is not necessarily going to have the same outcome.  Take care, and happy healthy pregnancies to all of you.
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Avatar_n_tn
My LMP was on January 2nd.  My HCG levels have been consistently doubling even tripling since my 1st blood test was done on February 8th.  I went for my U/S yesterday (2/20).  My doctor tried the transvaginal U/S but due to my weight and location of my uterus, he had a very difficult time.  Once he finally found the gestational sac and yolk sac, he stated I was only measuring at 5 weeks and 2 days.  I was devastated by the news as the gestational age should have been at 7 weeks.  I have VERY irregular periods and am not sure this is the cause of the difference in how far I am along.  I am scheduled for another U/S, but not for two weeks.  I am feeling wrecked by the entire thing and having to wait another two weeks is devastating.  Any thoughts?
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377493_tn?1356505749
Hey there,

Yeah, as someone who has been through this, I have some ideas for you....there are many reasons an ultrasound can date differently then LMP date.  You may have ovulated late, it may have taken a bit longer to fall down the fallopian tubes and inbed, you may be off on your dates.  It could also be the skill of the tech, or the condition of the equipment.  You could actually have another ultrasound same day, different tech and place, and hear a different result.   In my case, we weren't really sure there was a problem until my HCG's stopped going up.  7 weeks is very very early.  Also, in my case, I had spotted for 3 weeks.  There were all kinds of challanges.  So, I guess what I am saying is that the ultrasound in itself is not too serious right now.  I know how hard the waiting game is, it is the worst part, but unfortunately its all that they can do.  Try to take it easy (I know, easier said than done for sure), but stress really is one of the worse things that can happen.  And try not to worry.  I have heard of sooo many cases of this where all turned out just fine.

I wish you all the best, take care and good luck!!!
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