Paternity Uncertainty: Determining the Father of a Child

Question
Dear Expert,

Please help me in my confusion!

I had intercourse with a man on the 22nd March; the following day (23rd) I had my menstruation.
Afterwards some time (which unfortunately I do not remember when) I had one intercourse with my husband).
I found out on the 25th April that I am pregnant. According to the ultrasound of 5weeks and a half. And the due date is 23rd December 2008.

I am really questioning who the father is, because I have a strong 'feeling' that is the man I was with on the 22. In addition, I found out that during a menstruation can be that at the same time I was ovulating, and could have get pregnant at this moment. Is this correct?

Thank you very much for your time and effort.
Regards,
Isabel


Answer
While it is possible to ovulate while you are menstruating, this is very, very unusual.  If an ultrasound dated you at 5 1/2 weeks on April 25, then you would have conceived 3 1/2 weeks prior to that, putting your date of conception around April 4th and completely out of reach of your encounter on March 22nd.  Remember that conventional pregnancy dating assumes that you are "two weeks pregnant" the day of conception, because the dating runs from your last menstrual period and not your ovulation.