My son has recently slept with someone who now says she is pregnant to him.he has been seeing her for 7 weeks and 3 days.she had an ultra sound on the 9/9/08 which says she is 8 weeks and 5 days pregnant.Could my son be the father?

Uses and Accuracy of Ultrasound (http://www.babyzone.com/askanexpert/answer.asp?qid=194)

It seems to say the prior to 12 weeks... the way they measure is from head to rump. Most babies grow at the same rate for the first 20 weeks. So it is fairly accurate.

If I remember correctly the early the ultrasound is done, the more accurate it is, because of the development of babies organs and such.

In all actuality it is the 20 week ultrasound that is the most accurate. However, he will now have to wait until the baby is born and request a paternity test. All of pregnancy is a guessing game until the DNA proves one way or another.