pregnancy

I was wondering if it is possible for you too seem like your 15 weeks along (confirmed by ultrasound) but be 12 weeks? I have a friend who's girlfriend may have cheated on him. The doctors have said that the baby is developed 15 weeks as of this friday but they had sex on February 8th (it has to be then because that is when he lost his verginity). He may have gotten the date wrong and it actually been Februry 3rd, but that is still only 13 weeks. I would appriciate any help in explaining this.

Have a DNA test done when the baby is born. Then you will know for sure who the father is.