I am 22 yrs, sir I want to ask that I had unprotected sex with my girl friend on 11 Dec 2015 and she had her periods on 13 Dec which does not occur on due day due to some reason, we don't know and on 22 Dec 2015 she did pregnancy test (urine test) and the results are negative according to doctor, is there any chances of pregnancy now also or we are safe now. Is it possible dat the results may change after 1 week and they can be positive. How much possibility of change of result is there?