I saw an article today that claims:
"The rate of teen pregnancy in the United States reached a historic low in 2015 due to higher contraceptive use, according to a study published last month by the U.S. Centers for Disease Control and Prevention (CDC)."
However, it made me wonder if this is really the case. Perhaps in earlier years significantly more married couples were "teens". Though, for a lack of a better way to explain it, I think when most people think of "teen pregnancy" we think of a kid with a kid of their own. If we define "teens" as people who are still dependent on their own parents, how do the teen pregnancy rates of today compare to different eras/decades?
Family structures were different in different eras. I think that you will not get an answer defining teen as someone still dependent on their own parents.
Multi-generational households were more common in the U.S. before the rise of cities and are still more common in other cultures. Recent immigrants from those cultures continue to live in multi-generational households in the U.S.
In a different era a young married couple may be living with his or her parents working on a family farm or in another family business. Of course in that case the young married couple is "dependent" on their parents but their parents are also dependent on them as are grandparents and other members of the family. Everybody was dependent on each other.
Why would this young married couple with no experience leave one of their families? He may have grown up working on his family farm or could have been his father's apprentice learning that trade with the goal of taking over his father's business. She has never run a house nor raised children. It makes sense that they would live with, or at least near, family support for the purpose of raising their family.
Obviously this does not describe every family, but it describes some.
Maybe ask about pregnancies where the parents were under a certain age and the parents did not marry. Depending on the time, culture, and community pregnancy out of marriage had different outcomes for the woman and child. In some cases if the man stepped up and "did the right thing" nobody thought twice about it.