A great scientific research paper on when human life begins-
This site is not necessarily prolife but it's a great resource to use for embryology/fetology-
Secular Pro-life is another great resource. They have a facebook page too!
I just took a quick look at it, but it looks really good.
I'm going to print it out so I can underline & whatnot.
IMO, the key has always been (p.6),
"Is a human zygote a human organism?"
Unfortunately, 'organism' doesn't have a crystal clear def.
Also, it may be nitpicking, but I really hate when people say
that a fertilized egg is an egg (as if a frozen liquid is still
liquid) & there may be some good stuff on that too. :)