(Closed) LMP and ultrasound dates don't line up?

posted 4 years ago in Pregnancy
Post # 2
Member
854 posts
Busy bee
  • Wedding: May 2013

Do you know when you ovulated? LMP dates assume everyone ovulates on cycle day 14, which not everyone does. So if you ovulated on cycle day 24, 5.5 weeks is totally normal. 

Post # 3
Member
9823 posts
Buzzing Beekeeper
  • Wedding: September 2013

How long are your cycles? If you ovulated later (like PP above, maybe CD 24/25) it could be perfectly normal. LMP assumes you O on CD14

Post # 4
Member
7977 posts
Bumble Beekeeper
  • Wedding: July 2013 - UK

I had an early scan at 6+ weeks where they couldn’t even find a foetal pole, let alone make a reasonable guess as to how far along I was. Two weeks later, however, there it was, complete with a little heartbeat.

PPs are right in that the most common cause is late ovulation. Now, I have a fair idea when I ovulated because, although I was having annovulatory cycles, when I did occasionally ovulate then it was always on CD14. So it wasn’t that for me. However, I didn’t get a positive pregnancy test until several days after my period was due. I looked it up, and although many women implant early, implantation can take up to 17 days after ovulation and still be within the biologically normal range. Apparently there are many factors which can cause late implantation. This would also cause you to measure wrong on the scan. Schedule another scan for two weeks’ time and see what happens.

Post # 5
Member
96 posts
Worker bee
  • Wedding: December 2013

Mine were just over a week apart – I would have been 8 weeks exactly at my first scan by LMP, but I was 6+6 because I ovulated late (second cycle off the pill). I’m now 13+2 and everything looks good so far.

Good luck!

Post # 6
Member
9686 posts
Buzzing Beekeeper
  • Wedding: August 2012

Do you know when you ovulated? My scans were like 3 weeks off, but I knew when I ovulated and that my cycle was super long. I didn’t get a BFP until day CD 41!

Post # 7
Member
1341 posts
Bumble bee
  • Wedding: September 2005 - A Castle

This was me almost 9 years ago. I went for my first appointment thinking I was around 8 weeks but was really 6 and a few days. She’s sitting in school right now 🙂 

Post # 8
Member
2902 posts
Sugar bee
  • Wedding: June 2013

Sunshine09: If you’re sure that you ovulated on cycle day 14 (as in, you were charting or being monitored by ultrasound) then, sadly, it’s probably not good news. But if it’s possible you ovulated later than that, you could be just fine! LMP dating is only accurate if you ovulate on CD 14, so if you could have ovulated and conceived a week later than that, you might just be earlier than you thought! I have my fingers crossed for you. 

KinkyOrange:  I’m curious about the source of your information that implantation up to 17 days after ovulation is within a biologically normal range. My understanding, based on this New England Journal of Medicine article, is that implantation later than 11 days post-ovulation is very strongly associated with early pregnancy loss, and all three of the pregnancies where implantation occured after day 12 ended in pregnancy loss. (http://www.oocities.org/joann_fitz/AboutUs/ourchildren/infertility/articles/mc/implantationandpregloss.pdf) If you know of more recent research, though, I’d love to know about it! 

Post # 9
Member
7977 posts
Bumble Beekeeper
  • Wedding: July 2013 - UK

KatieBklyn:  I will confess that I did not get that particular nugget of information directly from PubMed, so I’m not 100% sure about reliability in comparison to your source. It’s been a while since I looked it up (and now, of course, I can’t find the flipping thing), but I do remember that it was based on information to do with false negative pregnancy tests, and possible reasons for them. The conclusion was that 17DPO was right on the cusp of biological normality… not likely, but possible. The average was 7-12 days, I seem to remember.

This was stuff I looked into at the start of the year, when I had my own scan and was given a gloomy outcome… I was never a day late in my life before I got pregnant, and always had 28 day cycles, so they were pretty certain of the dates… not seeing a foetal pole at all by that stage was bad news. However, like I said, two weeks later then we had a heartbeat, and I’m now preparing to deliver in a few weeks. I did have a praevia though, and my placenta is still extremely low, so implantation occurred right at the very, very bottom of the uterus.

I suspect there was quite a lot of luck involved in the whole process for me, especially with my ovulation problems.

Post # 10
Member
1341 posts
Bumble bee

I had the opposite, I was further along by about 3 to 4 weeks when comparing my LMP with ultrasound. 

Post # 11
Member
2902 posts
Sugar bee
  • Wedding: June 2013

KinkyOrange:  First, I’m so happy things worked out for you! That must have been pretty scary there, in the beginning. If you don’t mind some more nosy questions, does your due date line up with your LMP now, or did they date your pregnancy from the earliest measurments? 

Post # 12
Member
276 posts
Helper bee

If you ovulated late or have long cycles this is normal. My US was 8 days behind LMP but I have longer cycles and knew when I ovulated so the US date is what I expected. Anything within a week of LMP is considered normal according to my OB (assuming you don’t have long cycles or know ovulation date.)

Post # 13
Member
198 posts
Blushing bee
  • Wedding: July 2013

My LMP was 5 days ahead of my ultrasound date, but I had expected that given my long cycles. My ultrasound date matched the timing of when I thought I had ovulated.

Post # 14
Member
7977 posts
Bumble Beekeeper
  • Wedding: July 2013 - UK

KatieBklyn:  Not offended at all! And, By The Way, I’ve also realised I made a mistake in my earlier posts. Am I allowed to blame pregnancy brain, LOL? My implantation did not take 17 days… however, I didn’t get my BFP until 17DPO!

*herp, derp*

Therefore, assuming that it takes an average of 3-5 days after implantation for the body to start producing enough HCG to turn a pregnancy test positive, implantation would have taken 12-14 days in my case. Assuming the lower figure is correct (12 days for implantation) then that is what would place me to the far end of the biologically normal range. By The Way, I also have no problems believing that late implantation is strongly associated with pregnancy loss. I just think I got lucky.

In answer to your question, I got my first BFP three days after my period was due, on CD31 (I had been testing every day… it was driving me crazy!). My scan at around the 8 week mark showed me exactly three days behind LMP. Likewise, my dating/nuchal scan confirmed that I was exactly three days behind, so that’s what my due date has been based on.

Anyway, I just wanted to chime in on OP’s thread to show her that sometimes these stories do have a happy ending (and to correct my earlier **** up)!

EDIT: Of course, I do realise that none of this actually explains why I didn’t even have a visible foetal pole on the first scan. A few reasons were suggested to me, but they all boiled down to “at that stage, it’s very small, and mistakes can be made, especially if it’s in a strange position in the uterus, and especially if the US person is looking for something which is smaller than expected”.

Post # 15
Member
77 posts
Worker bee
  • Wedding: August 2014

With my first pregnancy I went for my dating u/s thinking I was close to 9 weeks pregnant. Turns out I was only 6 weeks. 

I actually had to go for two scans because the first one (I thought I was 7-8 weeks) showed NOTHING at all. So I had to wait a week or so and go back for the one mentioned above. 

For me it all came down to the fact that my cycles were totally irregular so it became nearly impossible to pinpoint dates until the dating scan was able to do so. 

I do remember that wait between the first scan and the second scan was excrutiating because I was convinced the whole time that I would go back and it wouldn’t be a pregnancy or a viable pregnancy or that it was all a figment of my imagination. 

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