“Many of us do not agree with the definition quoted if the implication is that life begins at some point after fertilization...”
Not every fertilized egg, embryo, ever makes it to implantation. That is why adult women have about 600 eggs stored away for potential use.
I think most people are aware of the basic biology. The question comes down to when human life begins.
But that (the natural attrition of fertilized ova) is a natural, God-given state of affairs, and no moral opprobium attaches to it.
The deliberate and willful harvesting and fertilization of excessive numbers of ova (10-20 per treatment) with the premeditated intention to "dispose" of a large portion of them, on the other hand, is definitely not in compliance with the natural order of things.
Regards,