That I do not get.
Outside of the fact that she got pregnant, what makes you think that they were not using contraceptives? Birth control pills fail, condoms fail, all methods of birth control, even a vasectomy, have been known to fail. That said, the thing with teenagers and raging hormones is they may not have ever intended to have sex but got carried away in the heat of the moment. Happens all the time. It happened in the 1950s when I was in high school and I am sure it happens today.
And nobody brings up the question, what if these two are NOT in love? Is it your opinion that they still must get married and raise this child together in what can only be termed a “loveless” marriage if so?
Especially nowadays when they’re being ‘educated’ about things in school, on tv, in newspapers and magazines, etc. There’s no excuse for not using anything.
Maybe they were using contraception. Condoms break, etc.