Well I think that the teenage pregnancy comes from the rather prudish culture that's put upon teenagers by adults. The adults make out sex and nudity to be sort of tabooish or at least something that teenagers aren't mature enough to handle (in a similar vein to alcohol). Being teenagers this just makes it a "forbidden fruit" sort of thing so they go after sex with even more vigor. The thing is since they aren't really "supposed" to be having sex (at least according to mainstream social rules), they are doing it without real interference from adults, so the teens probably aren't using protection properly or at all. Its sort of like alcohol; because its illegal for anyone under the age of 21 to drink alcohol here in the States, they due it without proper supervision and so its a lot more dangerous.
So its a combination of the "Forbidden Fruit" aspect of sex that's taught here in the US and the fact that teens aren't being properly taught how to have safe sex because they "aren't supposed to be having it". I can loosely compare it to the age of Prohibition that we had here for a while. Since people were still looking for a drink and alcohol was prohibited (in some way, I think it was illegal to sell or produce it), drinkers had to turn to illegal and more dangerous venues to get their alcohol.
So its a combination of the "Forbidden Fruit" aspect of sex that's taught here in the US and the fact that teens aren't being properly taught how to have safe sex because they "aren't supposed to be having it". I can loosely compare it to the age of Prohibition that we had here for a while. Since people were still looking for a drink and alcohol was prohibited (in some way, I think it was illegal to sell or produce it), drinkers had to turn to illegal and more dangerous venues to get their alcohol.