Instead, each one develops into a separate structure. This condition is called double uterus (uterus didelphys). A double uterus may have one opening (cervix) into one vagina, or each uterine cavity may have a cervix. There may even be two vaginas. Double uterus is rare and sometimes never diagnosed. The percentage of women with a double uterus is likely higher in those with a history of miscarriage or premature birth. The cause of double uterus is unknown.