At least some teens think that having a baby will give them emotional satisfaction. They feel that their baby will love them no matter what. They think that this will help them to feel more loved and accepted if they do not have enough affection from other sources.
In the beginning they may take pleasure in the attention, baby showers, gifts etc. But I seriously doubt that any teen can go through parenthood and not have some serious struggles. Finances, lack of freedom, medical bills etc are just a few realities that I'm sure most teens (and even adults) struggle with when they become parents.
I have heard of pregnancy pacts, where teen girls get pregnant because their friends do, or agree to get pregnant. I think they are rarer than the media makes them out to be. Most teen girls get pregnant by accident. They may enjoy some aspects of being a mother, but mostly they will regret missing out on the traditional teen rites of passage such as high school sports and prom. Having a baby may sound like fun, like playing dress-up, until you actually have the responsibility.
I think it is easy for teenagers to desire pregnancy and parenthood without truly understanding what they are getting into. We see in the media how "cool" it is to be pregnant. Often, teenagers have friends with children. It can seem glamorous and fun, but the reality of it is very different. Being a parent is a difficult task. Caring a baby during pregnancy isn't always a smooth, easy ride. I think many teens might want to have the life they think they see, but it is not reality.
Some girls who get pregnant struggle with the decision of whether to give the baby up for adoption or to keep the baby and raise it themselves, but once they make the decision to keep the baby actually end up being remarkably focused and driven. I have one former student who is a great mom and still managing her studies, but the key to this fortunate situation is the young ladies amazing parents who have provided her with what she needs to be successful.
Few teen pregnancies are planned, but based on my experiences as a high school teacher, I'd say that attention and the novelty of a baby are among the reasons that the few girls who want a baby make that choice. As the other posters have said, they are often surprised by the amount of dedication and pure effort it takes to be a parent, not to mention being a student and a parent.
I have had several students become intentionally pregnant after seeing the fuss made of a new mum and their baby. Girls who have had limited success and attention in their lives may see that making a new person is an achievement. A new baby brings a lot of attention - and demands a lot too.
some feel pleasure but most of them are afraid of that .