This is anecdotal evidence, but from my experience, girls get knocked up more by the guys they want to get knocked up by. Somehow, their minds transmit the message to their body that this is the guy they want to have a child of. Hence I believe a girl that is in love with you is more likely to be knocked up than some tinder slut or one night stand that doesn't really care about you.
Not sure if there is any science to back this up.
Not sure if there is any science to back this up.