According to my ultrasound my EDD is feb19/2013. I read that the 40 weeks is calculated from LMP. The first 2 weeks is the gestational period. That would be may15/2012, conception may29/2012. Is this the actual estimated time I conceived (may29th?) give or take a few days? My question is was the 29 th when I conceived? I am now 25 weeks and 1 day pregnant according to U/S. Does that mean the babies are 23 weeks and 1 day? That the extra 2 weeks are gestational? Also how long can sperm live in a women's body? I read 2-3 days and then 5-7 days? I had my period end may 16, and had sex that night. What are the chances that the sperm lived Max life spans of 7 days making conception may22 and making my U/S off a week? Can a transvaginal U/S be off 1-2 weeks? My first U/S was at 6 weeks 2 days.

If this is a question of paternity than the only option is a DNA test after the baby is born.

Ultrasound is a best guess and can be off as much as a month. There's no way to determine by ultrasound an accurate conception date when the dates of possible conception are only days apart.