A doctor can tell a girl has engaged in sex if she is pregnant, has a sexually transmitted infection or informs the doctor of her sexual history, according to TeenHealthFX. If the girl very recently had sex, the doctor may be able to detect traces of ejaculate, notes Scarleteen.
It is a myth that a doctor can tell a girl has had sexual intercourse if her hymeneal ring is broken, notes TeenHealthFX. Many activities other than sex, some of which include horseback riding, inserting tampons and playing sports, can cause the hymeneal ring to break, making it an unreliable indicator of sexual history.
Physicians sometimes examine the hymen when sexual assault is suspected in prepubescent girls because most very young girls still have intact hymens, according to Scarleteen. However, a knowledgeable doctor does not look at the hymen to determine if a girl who has begun puberty is sexually active as the hymen can break or wear away in many other ways and not all sexual activity is penetrative or vaginal.
When a girl becomes sexually active, medical care is needed to protect against pregnancy and screen for sexually transmitted infections. Teen health centers are available in many areas to provide young girls with reproductive health care, explains TeenHealthFX.