Hello, My period is 13 days late and it has never happened to me before. My hormone levels were checked by my gynecologist and endocrinologist several times of the past year and the results were always good, including the anti-Müllerian hormone. Last month due to my ankylosing spondylitis flare up, I was put on prednisone for 10 days (starting at 60 mg and then diminishing the daily dose). I felt fine afterwards most of the time, maybe a little tired. I did a urine test (the one you can by in a pharmacy for detecting early pregnancies) 3 days ago and it was negative. Soon I'll have to do an MRI and I am worried that I could be pregnant. How long do I have to wait before a pregnancy becomes detectable in a blood sample? My doctor said that urine tests can be wrong and that in some women hormone levels are too low for detection. I know that there is a slim chance that I might be pregnant, but I wouldn't want to do anything wrong. Anyway, could prednisone have caused this? Problems with the menstrual cycles were never mentioned. Could it be the early menopause? Thank you!