Being young and pregnant can create a great deal of emotional distress on the teen which is then transmitted to the baby. Many teens fall into an emotional crisis that they end up not wanting to have the baby.
Depression may arise when a teenager is pregnant. The teen may fall into a depression while trying to handle the emotions a pregnancy creates and all of the possibly negative feedback about the pregnancy from friends and family. The fluctuating hormones that a pregnancy causes may also prompt depression.
With all these emotional issues a rational behavior will make them attempt against their own life and try to self-abort.