I wouldn’t jump to the conclusion that Bristol’s pregnancy is her mother’s fault, but I certainly wouldn’t rule out the possibility that her mother’s teachings had an effect on her choices when it came to sex. I had a cousin that got pregnant at the age of 17 because her boyfriend (now husband) didn’t believe in the use of condoms. He knew what they were, how they worked, had the means and knowledge of how to acquire them, he just didn’t believe in using them because he was raised Catholic.
It’s anecdotal, sure, but the lesson is, knowledge of birth control methods isn’t always enough to get a kid (or even a young adult) to use them. A parent can endorse their use while not endorsing promiscuity, and it can go a long way on influencing the choices their child makes.