It depends on what you mean by "alive." One can argue that an embryo and then a fetus are alive otherwise they would not be developing. They are alive because they must physically depend on the birth mother to sustain them. How is that different than an individual who encounters a terrible accident and must stay alive with the help of an artificial respirator or other life support device?

The one incredible thing about medical science is how rapidly it has progressed particularly in the issue you raised about premature babies. I would imagine that there would be a time soon where they will have the ability to extract an embryo or fetus and have the means to incubate them to full term.