Most babies with any sort of monosomy--or trisomy, for that matter--are miscarried or stillborn. The vast majority of babies conceived with Turner Syndrome won't make it to birth. Apparently, that's actually one of the controversies with early amniocentesis. Not only is it more dangerous, but it can detect a problem in a pregnancy that was going to end in spontaneous abortion.
If an amnio shows, for instance, trisomy 13, the parents will have to do a lot of soul-searching and might decide to end the pregnancy when if nature had taken its course, a miscarriage might have happened soon.