An imperforate hymen is a rare vaginal anomaly in which the hymen totally obstructs the vaginal entrance.
The frequency is low: approximately 0,1% in female newborns.
Sometimes this is discovered shortly after birth, but some girls only find out when they reach puberty and the menstrual blood is prevented from exiting. Sometimes it’s found earlier when a girl has other complaints and is examined.
If a girl has an imperforate hymen it can be opened surgically. This should be done before menstruation begins.