It all depends on the teenager, the majority are classified as low risk pregnancies. However, many of us have unhealthy lifestyles ~ ie: eating habits, sleep patterns ~ and bodies that have still not reached adult size/development, and these get plunked into higher risk.
My nurse told me that the same goes for people who are under 16, have been involved with drugs or the police, CAS/CCAS, have dropped out/not completed high school, or have underlying health problems. These people are the "most likely" to lead an unhealthy lifestyle while pregnant, lack education about pregnancy, not seek prenatal care/start prenatal care later in pregnancy, and/or develop complications.