SO PLEASED  to see Goodbye to Goodbye mentioned. It is quite simply an outstanding Drama, built around the relationship between the pregnant teen and the mother of the baby's child.  One of two Dramas that I have scored as 12/10 https://mydramalist.com/list/O38nwv91

Not a drama but a movie called My Palpitating Life. The leads get pregnant in high school but it’s set years in the future. There is frequent flashbacks to when they were in school and before the baby is born.