In discussion of miscarriage, the word viable often gets tossed around, but sometimes it can be a confusing word.
If a pregnancy is concluded to be "not viable," that generally means that the pregnancy cannot go to term and cannot result in a live baby being born. Some pregnancies are predestined to be nonviable, such as ectopic pregnancies, but others might be nonviable because the baby's heartbeat has stopped.
"Viability" can also be used to describe the point in pregnancy after which the baby could have a chance at survival outside the womb if born prematurely. Most doctors consider 24 weeks to be the cutoff point for viability, because babies born before 24 weeks generally have a poor prognosis.