My girlfriend had ultrasound done today 1-21-10 doctor says she is 15 weeks and 5 days aprox when she had sex it was a one time deal can some tell me aprox

My girl friend had ultrasound done today 1-21-10 doctor says she is 15 weeks 5 days can some one tell me when she had intercores

Well I would think that would be something that you need to ask for friend about, just because the U/S said she was 15 weeks and 5 days means nothing really.
If it was a one-time-deal she would know when she had sex.