Help conception confusion and ultrasound dating...

[Alice535]

My question is can an ultrasound be off by a whole months cycle? Especially if done so early in the first trimester?

Blood test done 19th sept 2-3 weeks pregnant.

I had a ultrasound done 20th sept dating me at 4w 5d. There was basically an empty uterus but a cyst was in there. I didn't tell my doctor my last LMP I wanted yo be sure on the Us that it works. He said your LMP should be 18th august he was right I had a 5 day bleed then which I'm sure was just like my normal period.
I went back two weeks later and measured 6w5d saw a little jelly bean and a heart beat.
I had more US at 8-9 weeks 11 weeks 13 weeks 15 weeks 18 weeks. All measuring to the same due date given at the first US that matches to my LMP. May 25th.

So conception he said was 1st sept.

I'm not 31 weeks.

Is it possible that the bleeding could of been implation and they mistaked an 8-9w pregnancy for a 4-5 week one and that I was pregnant from my last cycle? And that all ultrasounds have been out by 4 weeks to a month?

Could this pregnant be from intercourse on august 2nd? I know sperm can live max 7 days so I took that into account for Aug 9 latest time of conception and still leaves a huge 3 week gap from the latest I cab conceive from that encounter and from the earliest I can conceive from my US and LMP 28 Aug.

surely if they are wrong I'll be due April 25th? Not may 25th ...
Could I really be 35-36 weeks pregnant and not 31 weeks.... I don't feel that far along.

If she comes close to her may due date can we rule it out? Thank you.


** before bashing me I used a,condom that night, it broke. I was separated from my current partner. And I couldn't get morning after pill because it was abroad. Got back with my current partner from the 12th august until present day.... Please help

[Alice535]

Sorry I meant im now 31 weeks.
My period august 18th was supposed to come July 31st but I'd just started cortisone shots and meds and read they can delay or even skip ovulation that month and throw off periods. thanks 😄

[Userloser]

Oh sweetie! I really don't know! But I'm sure someone will! Hope you're having a happy and healthy pregnancy

[MrsBobDylan]

You'll be whatever they say you are in terms of weeks - are you worried this baby isn't your partner's? You would be better to focus on your pregnancy and look to get a paternity test after he/she is here. You can't change anything now and need to just focus on the arrival of your lovely baby.

[Alice535]

Thank you for answering. I know about a DNA test but its almost impossible I cannot tell my oh about the other encounter as that'd be the end even if we were seperated and he lives abroad too I'm in the UK so not sure how I'd do DNA

[WelshMammy123]

I'm sorry but I would trust the scan dates. They base their measurements on average foetal size and development and are very unlikely to be out by 4 weeks. I know that's not the answer you want to hear.

Has your partner not been at scans so not clocked the due date given by the scans?

As a pp has said the only option re paternity is a DNA. To be honest in my mind if there's a shadow of doubt then irrespective of when baby arrives you should consider that option.

Surely your partner would be understanding if it happened when you weren't together? Obviously then the choice of whether he can stay with you is then his alone to make. Appreciate it would be difficult for him but if you weren't together you weren't actually unfaithful to him x

[Alice535]

Hi no, actually all the scans due date and LMP all add up to it being his! Its the other guy that is a whole month before. would you really think Dna is needed? I don't think so especially if baby does come around r even later than expected dye date because if it was from the early august incident shed be due April 25th and that would make her 4-5 even 6 weeks past 40 weeks if she came around her may 25th due date given! Thank you

[Alice535]

I'm panicking because I read ultra sounds can't be used to determine paternity as can be out by about a week and sperm can live 3-7 days but even taking all that into account it just doesn't add up to august 2nd at all....

[Alice535]

I have answered underneath xx

[WantToGoingTo]

Ultrasound dating at 12 week scan is the most accurate dating method as foetuses tend to grow at same rate at that point. Later scans are not accurate in terms of dating as foetuses grow at different rates hence the different size babies everyone has! My mum is an obstetrician and says that 12 week scan is most reliable for dates unless you know lmp and ovulation date (e.g. Were doing opks and temping). I would say can't be the month earlier sex as scans are never out that much compared to lmp. Max difference is about a week.

[WantToGoingTo]

Also if you had a period on 18 August impossible it could be from sex on 2 August. Implantation bleeding isn't that common either and usually just a little spotting normally brown and couldn't be mistaken for a period

[Alice535]

Thank you so much, great information!
I don't think I had a 12 weeks but I had an 11 week and few days I think then one at 13 weeks and a few days. We watched it so closely with that many scans, ap the doctor did say in these weeks all baby's develop the same. So impossible to come in and find a 4-5 week scan actually be a 8-9 week scan. Especially since there was nothing on the first us then at the 6 weeks 4 day one there was a HB and tiny foetus. I think as long as she comes around her due date rather than early may I can rule it out? DNA test is really off the cards for a while I do know both blood groups too, so hopefully If she does turn out with one blood group we can be sure. I know that's not reliable as maybe she will take mine but .... I think I should relax thank you

[eurochick]

I think you're fairly safe. A scan at 4-5 weeks should just show a sac. At 8-9 weeks there should be limb buds on a little alien-like creature. They look very different.

[Alice535]

Great! I'm changing midwifes and have a phone call Monday I will ask her about this, however don't want her thinking bad of me really as shell be delivering etc. Do you think she will tell me the same? Surely they back up that their methods are accurate.

[TurquoiseDress]

Your dating scan is the one they do at around 11-13 weeks of pregnancy and it's meant to be the most accurate in terms of dating the pregnancy.

Apparently, as the pregnancy goes beyond the first trimester, the accuracy in terms of dating is less compared with the dating scan, but scans are still very accurate.

I really doubt they would be a whole month out with your due date.

Conception can be tricky to calculate just based on LMP and when you had sex- despite all the methods/tests, it's hard to pinpoint exactly when you ovulated.

Sperm can live for a good 5 days or sex, so the date of sexual intercourse doesn't mean much with respect to the date of actual conception.

Good luck with the pregnancy

[sn318]

@Alice535 ... I know this is an old post, but, if by chance you see this... were your scan dates accurate?