Coming-of-Age; Young Adult Literature
If coming-of-age stories tend to focus on the transition from the teenage years to adulthood, Kristina's tale is sort of this genre on steroids. After all, you don't get much closer to merging into adulthood than making a bunch of bad decisions before becoming a mom at age seventeen.
Actually, maybe "merging" is a poor choice of words. Try being slammed into it face-first. And while it's definitely not a happy story, there's something moving about the redemptive decision Kristina makes to keep her baby rather than have an abortion. While she says at the end of the book that she's "not really sure how this story ends" (Happy Endings.1), it's obvious that she's learned a lot about herself and how deeply choices can impact your life. For more about whether Kristina's really learned her lesson or not, check out the "What's Up with the Ending" section.
As for the young adult lit genre, a teenage girl sits at center stage of this story, narrating her own experiences in her own words. While she has an exceptional experience in some ways, in others she's navigating classic teen stuff like the desire to rebel, trying figure out who she is, confusion about dating and romance, and all that good (okay, it's often terrible) stuff. Everything about this book is designed to appeal to YA readers, from its main character to its subject matter to its creative poetic writing style.