Not all embryos are at all likely to implant, let alone make it all the way to babyhood. This video is about an interesting development in predicting which ones are going to make it, but it also has some useful numbers— particularly that only about one in three embryos can come to term.
This, obviously, is a strong argument that legislation predicated on the notion of "life begins at conception" is foolish. The most typical fate for a fertilized egg is death.
More detail available at KQED: Gabriela Quirós - In the Race for Life, Which Human Embryos Make It?