After sexual intercourse, the intact hymen usually ruptures

The hymen is a fold of mucous membrane, about 1 mm thick, situated at the vaginal outlet. In a prepubeal victim, vaginal penetration usually results in tearing of the hymen in the posterior 180deg, i.e. Between 3 and 9 o'clock position. Ref - Krishan Vij textbook of forensic medicine and toxicology 5e pg : 315