It totally depends on what state you’re in.
In WV, for example, the age of consent is 16. And it’s not referred to as “statutory rape,” it’s varying degrees of sexual assault.
1st Degree sexual assault would be if a 14 year old (or older) had sex with someone age 11 or younger.
3rd Degree sexual assault means that someone 16 or over had sex with someone 4 years or younger – and that someone has to be under the age of 16.
So it would appear that the State of WV gets extremely pissed off if one of the parties is younger than 12.
However, if a 16 year old boy sleeps with his 14 year old girlfriend, he couldn’t be prosecuted for anything AFAICT, even though she’s not of the age of consent.
If a 20 year old guy slept with a 15 year old, though, not OK.
Which is kind of weird if you think about it. In the first scenario, we’ve got a 14 year old having sex and we’re not going to do anything to her partner. We will, however, nail the guy in the second scenario even though he’s sleeping with someone older than the girl in the first scenario. Basically the state is contradicting itself: the age of consent is 16, but if you ignore that we won’t nail whoever’s nailing you provided they meet certain age requirements.
I guess they figure the greater the age gap between the two parties, the more likely that the older person has some kind of control over the younger?
So going back to the situation in the OP, someone getting a 12 year old pregnant may not be considered statutory rape – if a 15 year turned out to be the father, he’d probably be off the hook as far as any criminal charges go.