If it says I am due on dec 2nd then why do they say count 38 weeks instead of 40 and from the ultrasound it says I am 10 weeks today wouldn't you go back to week 0 to see when you are pregnant? I don't really have 2 weeks to spare I guess you would say so I am really confused

Well you need to find those two weeks.

When the doctor gave you the original estimate.. and it was only an estimate.. there was a 2 weeks plus or 2 week minus fudge factor because its not an exact science. So unless you had an Invitro procedure... no human can know the exact date of conception.

If those two weeks are to know who the father was... its too close to call and a DNA test will have to be done to establish who the father is.

You see, gestation is based on a 28 day cycle. Not every woman has a 28 day cycle, and not every cycle is 28 days, if that makes any sense.

Many women ovulate approximately 2 weeks after the first day of their period, LMP. However, since not every woman is the same, and we don't have a built in camera in the fallopian tube to see exactly when the egg is fertilized, we can only estimate using a mathematical calculation.

While you may have a regular cycle, unless you have been tracking ovulation for 6 months to a year using the basal temperature method, your doctor can only estimate according to the calculation method.

I don't understand why you say you don't have 2 weeks to spare. Are you going to die in those 2 weeks? If not, you certainly have 2 weeks to spare.

If paternity is in question, you will have to have a Jerry Springer test, better known as a paternity test, to determine who is the father.