About 15 to 20 percent of known pregnancies end in spontaneous abortion (before the 20th week of gestation) or miscarriages (after the 20th week). The failure of conception to result in a live birth is a common and natural event.Of course, this is a non sequitur. It does not follow that if some unborn human beings die by natural causes, it is therefore permissible to ourselves intentionally cause the death of unborn human beings. For example, the fact that a natural disaster, such as an earthquake, claims the lives of thousands of people does not justify the Holocaust. The fact that my father could well die from a heart attack at any time does not justify his murder.
There's no reason why human aspiration and necessity shouldn't also be a factor in determining whether or not a particular pregnancy is brought to term by potential parents.
Miscarriage (natural death) does not justify abortion (intentional killing).