I was actually asked in one argument when in the fertilization process rights arise. Obviously it's when the genome is finished forming, but let's assume the question was hard. What would that mean?
It is important to define life begins so that no one is denied their rights, so iffy some-time-in-gestation philosophies don't cut it. But there's no method of contraceptive or abortion that happens during fertilization.
The question, practically speaking, is meaningless.