M.P.
If your last pregnancy with the same father resulted in a miscarriage because of trisomy, then it is possible that this one will too. You need to consult with a genetic counselor to know what the odds are.
Your doctor is the only one who can answer this question. I urge you to see a genetic counselor before attempting any further pregnancies if this one fails. You do not need to suffer this sort of loss and fear.
I don't know what the 1/49 means. Are you saying the odds were 1 in 49 that you would have a baby with trisomy or 1 in 49 that your baby would be normal? If so, only you know if you're willing to take the chance. And, I suggest the odds would be the same for this pregnancy if it's the same father.
In regards to the subchorionic bleed, did you google those specific words? I found several sites that discussed that condition. However, if your question is what are the odds that this subchorionc bleed will result in a miscarriage, I don't think there is any way of knowing. Time will tell. I know that's not what you want to hear. Ask the doctor to be sure.