Until about 1856 the Church did not consider a fetus, let alone a zygote, "a person." It frowned upon abortion as it did masturbation and contraception actions discouraged as interfering with procreation. Prominent theologians maintained that the most valid justification for sexual activity was procreation. This intent reduced the sinfulness inherent in the pleasure.
How many fetuses can fit on the head of a pin?
There's a memo I'm glad I didn't get.