Every ova and every sperm is a potential human.
No, they aren't. The combination of the two is a potential human, the two alone is nothing. You'll never make a human being with only half a working genome.
When is terminating a pregnancy equivalent to murdering a baby?
Always. Sometimes it's okay to kill things. I only ask that people accept they're killing them. It's like eating meat without accepting you're killing an animal or sentencing a rapist to death without admitting you're killing him.
Abortion isn't good. It's death. It's killing something that is alive. You are ending its life. When I eat a burger, I understand that I killed a cow. When I go hunting, I understand I'm putting a bullet through the heart of a deer. It's amazing how difficult it is for "pro-choice" individuals to accept that they are killing a human. I get it if you're for it. Just own it. "I want to kill humans in the womb" It's not a big deal to just admit it.