Hymens can come in different shapes. The most common hymen in young women is shaped like a half moon. This shape allows menstrual blood to flow out of the vagina. Imperforate hymen : An imperforate hymen can sometimes be diagnosed at birth. More often, the diagnosis is made during the teen years. An imperforate hymen is a thin membrane that completely covers the opening to the vagina.
The hymen is a piece of skin covering the vaginal opening in females. In about the 3 rd or 4 th month of pregnancy, the hymen in female fetuses begins to form. It remains intact until it is broken by most often sexual intercourse. It can also be broken by activity or the insertion of something into the vaginal canal.