Are ultrasound conception dates accurate?

[tina6146]

I discovered I was pregnant unexpectedly, and went to have an ultrasound on May 23rd. Due to having wavering periods, I never really keep track, and therefore I don't know when my last period was. I can give an "estimate" but I really don't know because I never keep track. (Plus I have always been told that because of metabolic issues, and PCOS that it would be very hard for me to get pregnant).
Anyway, not exactly proud of this, but I was with 2 different men in a two week time period. One I didn't use protection with on Saturday April 7th (we have been very good friends for years, and it just happened on a night out drinking/dancing) and the other man I only went out with a few times, and when we slept together the following week (on Saturday April 14th), the condom broke. I didn't think anything of it, because I am almost 38, and this has never happened to me before.
So, my question is, when I went to have my ultrasound, the sonographer did 2 measurements for the conception date: one was 6 weeks and 3 days, and the other one (just to be sure) was 6 weeks 5 days. So, we split the difference and said 6 weeks 4 days. This would make my conception date April 7th, which is the exact night I was with the first man.
Do you think there's a big chance that the 2nd man could potentially be the father? I am hoping the first man is indeed the father, because we have been friends for years, and it would be alot easier to handle. The second man, however, I don't even speak to anymore. I would hate for it to be the second man.
Any advice on people that have gone through this? I guess I just want some confirmation that these ultrasound dates are accurate. The ultrasound tech was amazing, and I feel like she really knew what she was doing, but I just want to make sure that these results couldn't be a whole 7-8 days off.

[boontew]

Thank you for your response
She went to the clinic on Feb 12, the doctor told her that she had miscarriage as nothing shown up on the ultrasound. I was thinking this is because she told that her LMP was on Dec 15 which put her 2w more. She waited few more days then had another one on Feb 16 only then it can be seen in the us. Was it too early to have an ultrasound scan on Feb12. But there is only 4 days gap though. Does it make more on dating the coception?
I am confident that the baby is mine but I was wondering how the plan B failed. Is it because she took it too many times in a month? How the plan B work in delaying the ovulation? What makes her cycle longer than normal cycle she had before?
Thanks again.

[AnnieBrooke]

Ultrasounds are more accurate at 6 weeks for this purpose than at 10 weeks, and the way she is taking Plan B, she would certainly have irregular cycles that could not be used to count forward from to determine a conception date.  By 10 weeks, an ultrasound could be several days off for dating purposes.  Sex prior to January 6 would probably be too early to produce a baby.  In your shoes I would operate on the assumption that the baby is yours, but would do a DNA test once the baby arrives just to put the question to rest forever.  

[boontew]

Annie,

My gf and I had sex on Jan 14 and Jan 15 a lot of times. She found out she is pregnant on Feb16 and ultrasould put her 6w1d pregnant which saying she conceived on Jan 18. But when she had her second ultrasound on Mar 10, ultrasound put her 10w3d pregnant and conceived on Jan 11. She told me that she ate Plan B on the Jan15 evening.
She admitted that she had sex with another guy, didn't tell me when, but it is before Jan6 as I was still with her that day. I left her for work on Jan17 again, not sure if she was with the guy again or not.
What is the odd of the baby being mine if she did had sex with the other guy on Jan5? I am hoping the baby is mine and I can forgive what she did, if the baby is not mine, I will ask the guy to responsible for it for the good of the baby. Btw, her LMP was on Dec15 but only last for 2 days. She had irregular cycle as she took Plan B few times in a month. Should we go with her LMP or ultrasound? Is it possible that the Plan B on 15 did not take effect as we had several times of sex on the 14 itself? How accurate is the ultrasound on 6 and 10 weeks?

Thanks

[doomed23]

Thank you for your response, you've been a huge help!!!

[AnnieBrooke]

Well, you are not in a good spot to know who the father is without a DNA test, unfortunately.  
1.  Condoms are only 80% effective
2.  Sperm can live in the woman's reproductive tract 5 or 6 days
3.  The midwife gave you a weeks date (if she said 11 weeks 0 days) and an estimated due date on a certain date, and the dates were not consistent each other
4.  Your period did not correspond to your ovulation according to the midwife [is your period always exactly a certain number of days from the previous one without fail?]
5.  You had sex with two men close enough together that if there was condom failure they both could have had living sperm in your body at the same time
6.  Your earliest ultrasound wasn't early enough to pinpoint when you got pregnant with the precision you need, and any you get from now on could have a larger margin for error

I would not hesitate to use either Ravgen or the DDC, if you test with both men.  I would recommend Ravgen over the DDC only because I have never heard a credible complaint about them.  I have only heard one credible complaint about the DDC, and out of the huge number of tests they must do, that is not a lot.  In your shoes I would not hesitate to test using either lab.  

[doomed23]

And condoms were my choice of contraception the last week of August.