Most of the female reproductive system comes from two structures, known as müllerian ducts. These ducts become the fallopian tubes, uterus and vagina in females.
They form into reproductive organs during the ninth week of pregnancy. In rare cases, the "fusion" or "duplication" of organs can occur. For example:
- In uterus didelphys, there are two each of a uterus, cervix and vagina. One vagina is blocked, and the other is unblocked.
- In uterus duplex bicollis, there are two uteruses and cervix, but only one vagina.
- In bicornate uterus, there are two uteruses fused with one cervix and one vagina.