sex ed 101:
When a man and woman get together sexually they do so to have either pleasure or a baby. Both men and women have reproductive organs... Women have what is called a v****a and men have a p***s. The male species have a single tiny cell that clings to millions of other single tiny cells called sperm. This sperm swims to the egg during intercourse and attempts to impregnate the egg.
Now before the egg is fertilized the egg is just an egg and up until the sperm penetrates the egg... the sperm is just spermatozoa or seminal fluid. But obviously because God made us to procreate this way... The egg is a potential baby and the sperm cells are potential babies...
But not until actual fertilization or conception as it is also known to be called is it actually a baby. New life does not begin until CONCEPTION.
As for your question.... It comes down to Intent... If you intend on getting pregnant and you do something to inhibit the process then yes it is killing babies... According to God; in the story of Onan in the Old Testament. Link
This is my view and I'm sticking to it.
Braylan