Possible Pregnancy: Negative Test, Still at Risk?

Question
My first day of period was 01-19-2008, and I had unprotected sex last 01-27 and 28, 2008. I had pregnancy test last this morning and it was negative. Is it still possible that I could be pregnant? My cycle lies between 28-29 days. Thank You.

Answer
Until you have reached the expected day of your next period, you cannot be certain that you are not pregnant, even with a negative pregnancy test.  Home pregnancy tests measure the amount of HCG in your urine.  This hormone begins to be produced at conception and gradually increases throughout the first trimester.  However, the exact amount produced varies greatly from woman to woman.  Some women can get a positive result as early as 7-10 days after conception, but other women do not get a positive test until their period is a week late (or more!).

You might be able to get a more definitive result by getting a blood test done through your doctor's office.  Blood tests can detect a much lower level of HCG than urine tests, and will show a positive result much more quickly.