The old rule was if a girl is sexually active she should have a GYN check up, which included a Pap smear. Now, there is a belief that most young girls who show abnormal cells self correct and a follow up pap is often negative. So, the recommendations now are less aggressive, but I have my own feelings about that. I think girls should go to the doctor when they become sexually active. There is a plethora of STD’s and young girls are less likely to report symptoms.
Some STD’s are symptomless in some women and wreak havoc on fertility. So, teens who are active should have cultures done and a Pap in my opinion. Especially Chlamydia, one of the ones that can have no symptoms or mysterious ones. Girls and women often have discharge complaints dismissed by other adults or even doctors. Pain in the lower abdomen can be dismissed as cramps, growing pains, digestive, etc.
Chlamydia does not show up on a pap nor a regular culture. It needs a separate specific culture done.