I have had two unexplained miscarriages in arow am now pregnant again what are the chances of having a 3rd aged 23?

Higher than usual. All things being equal, your chances of miscarriage with this pregnancy is slightly higher than that of other women your age. But because you are young, you also have a higher chance of a successful pregnancy, especially if you're healthy. If not done already, your OB should get an HCG level, pelvic exam and ultrasound. If everything looks good, chances are you'll have a healthy a baby.