Dating is from a conception scan need

Are ultrasound conception dates accurate?

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.
Read more
Thank you so much for the reply.  I honestly don't know when ultrasound was done.  I imagine it was done around the typical time (12-18w?) and her date hasn't changed.  We have been talking off and on about this and I recommended a DNA test.  She has been reluctant until recently to get this.  But, still hasn't done anything yet.  Its hard for me to move with my life worrying about this. I don't want to get into another relationship with someone that I may care about and have the "its your baby" thrown in.  I suppose my question is that based on EDD of 2/11/16 and the times we had sex, there is a possibility that I could be the father correct?  According to online calculators it puts the ovulation around 5/21.
Also, she did a ovulation test 5/26 which was positive.  I found were a positive ovulation test could mean positive pregnancy as well.  Im so confused.  If there is a decent chance based on EDD of 2/11, then I would like to press her a little harder to get the noninvasive DNA test now.
sorry to keep adding to the discussion thread.  I feel the EDD is accurate because it was confirmed by a mutual friend and probably done around mid July. This is going to sound odd, but the reason I am accurate with my dates, is that we were actually trying to get pregnant since January and we were keeping track of her cycle.  In fact, I have in my records that she had some spotting 5/9, then a period 5/14-20.  The previous periods that I have were 2/13-17, 3/13-18, and 4/8-15. Negative preg test 4/22.

Do you think based on this there is a chance I could be the father?  I realize its mostly speculation and only a DNA test will exclude me.  Are the noninvasive tests that swab my check and match it against fetal cells in her blood reliable?  I'll shut up now and await your thoughts.
Dear annie. well my wife was cheating on me and is now living with the other man. The problem is we had protected sex 16 nov. She went for an ultra sound 12 dec and the ultra sound said that the conception date is 16 nov. By the she has been sleeping allot with the other man. I want to know if it is possible that the baby can be mine.
Dirkestan, I might have not been very clear.

1.  IF the date for conception is right, then you do have a chance to be the dad, because condoms only have about an 80% effectiveness rate.

2.  The way to know if the date for conception is correct is to analyze where it came from.  If the doctor looked at the ultrasound and offered this specific date, and said it is the conception date, that suggests accuracy.  Did he say she was 5 weeks 5 days 'pregnant'?

If the doctor gave some information and then your wife figured out the conception date on her own, (or you did), then that is not as useful because it could be based on misunderstanding what the doctor did say.
Dear Annie,
I was dating another man the month of August and moved states September 1st and found myself in another relationship. September 1st - 4th I had what I thought to be a "period". September 27th I took a pregnancy test and had a positive result. However, I had an ultrasound with a midwife November 4th and she stated I was 11 weeks along with a due date on May 24th, which made it impossible for me to have had a period the 1st of September (according to her). With my period having been on September 1st my due date should have been June 7th NOT May 24th, but at my first ultrasound having a due date of June 7th would have put me at 9 weeks along NOT 11. If you could give me your input on whether you believe I conceived in August or September that would be great, I'm pretty torn up about this and researching different prenatal paternity test options. Is there any way my midwife is wrong about her dates? Thank you.
Sorry, did you say your first ultrasound gave you a due date of June 7 or May 24?
The ultrasound gave me a due date of May 24th. Thanks for responding.
At what point in the pregnancy was the ultrasound that gave you a due date of May 24, was that at 11 weeks?
I was just a little thrown by you saying "but at my first ultrasound having a due date of June 7th would have put me at 9 weeks along NOT 11."  
I guess I'm also a bit thrown by this part  " I had an ultrasound with a midwife November 4th and she stated I was 11 weeks along with a due date on May 24th."  If someone had an ultrasound on November 4 that said she was 11 weeks 0 days, she would be due on May 28, I think.
Yes, my midwife told me that I was 11 weeks along on November 4th. On that day she calculated that my due date was May 24th. Even though I told her that i had a lmp date of September 1st.
Anyway, if you had sex before coming to the United States as late as the last couple of days of August, and then had sex once arriving in the United States as early as, say, September 4 or 5, an 11th-week ultrasound will not help you decide who is the dad.  Sperm can live 5 or 6 days in your reproductive tract, and by week 12, most doctors doing ultrasounds for purposes of determining conception will say "give or take 7 days."  (By the time you are at 40 weeks, the margin for error will be +/- 3 weeks.)

If you didn't have sex with Mr. Home Country in the last week of August, and if you didn't start up with Mr. USA until perhaps the second or third week of September, you could speculate with perhaps some certainty that the baby came from Mr. USA.  But if you did have sex with both guys within only a few days or a week, you will need a DNA test.  Prenatal DNA tests are available from two good labs (that I know of) and several charlatan labs that will just waste your money.  If you want to go the prenatal route, try Ravgen or the DDC.  Both have affiliate labs all over the world, I believe.  The cost is about ten times higher than if you had a test after the baby is born, but especially if you test with both guys, you will get an answer.

I did not have unprotected sex with the significant other I had during August during the last week I was there, however I did have unprotected sex with the guy from the month of September multiple times from September 1st until the 7th.