Oh, that's a sad question. I am very sorry about your loss. I don't think there is a 'most common' time during the first trimester but the first trimester (13 weeks and under) is when the vast majority of miscarriages happen. My doctor always said if you make it past week 13, you would most likely not have a miscarriage. 1 in 4 pregnancies ends in miscarriage so it is sadly pretty common. Hang in there. Again, so sorry for your loss.