Double vagina, synonimically called longitudinal vaginal septum, is a congenital abnormality of the female reproductive tract. During embryonic development, a vagina is usually formed by the fusion of two tubes, called Müllerian ducts. If they fail to fuse in the vertical plane, the longitudinal vaginal septum develops, resulting in a double vagina (Pic. 1). There may be associated duplications of the more cranial parts of the Müllerian derivatives, a double cervix, and either a uterine septum or uterus didelphys (double uterus). 

The person with a longitudinal vaginal septum may be asymptomatic and not aware of the condition. It may present clinically as a difficulty in inserting tampons, persistent bleeding despite the presence of a tampon, or dyspareunia (pain felt during sexual intercourse). Women with this condition have also an increased risk of pregnancy and delivery complications, such as early pregnancy loss, miscarriage and premature labor.

Double vagina may be associated with several diseases including: 

Uterine malformations

Women with double vagina are likely to be affected with some other associated duplications of the reproductive tract, sumarilly called Müllerian duct anomalies. Mullerian duct anomalies (MDAs) are congenital defects of the female genital system that arise from abnormal embryological development of the Mullerian ducts. Uterus is commonly affected, being either partitioned completely and existing as two separate organs (called double uterus, uterus duplex, or uterus didelphys) or only partly, creating an uterine septum (or uterus septus). 

Uterus septus (septate uterus, uterine septum)

Resulting from incomplete Müllerian duct fusion in the uterine region, a septate uterus (or uterus septus) may develop (Pic. 2). Septate uterus is the commonest uterine anomaly with a mean incidence of ~35%. The wedge-like partition may involve only the superior part of the cavity resulting in an incomplete septum or a subseptate uterus, or less frequently the total length of the cavity (complete septum) and the cervix resulting in a double cervix. It is generally accepted that having a uterine anomaly is associated with poorer pregnancy outcomes such as increased chances of spontaneous abortion, premature labor, cesarean delivery due to breech presentation, and decreased live births, compared to a normal uterus.

Bicornuate uterus

A bicornuate uterus or bicornate uterus, commonly referred to as a "heart-shaped" uterus, is a uterus composed of two "horns" separated by a septum. In humans, a bicornuate uterus is a type of uterine malformation. It is formed during embryogenesis, when the upper parts of the Müllerian ducts fail to fuse. As a result, the lower part of the uterus is unitary while the upper part is bifurcated.

Uterus duplex (uterus didelphys, double uterus)

Uterus duplex (or uterus didelphys) represents a uterine malformation where the uterus is present as a paired organ when the embryogenetic fusion of the Müllerian ducts fails to occur (Pic. 3). A didelphys uterus is one of the least common among MDAs. Most women with a didelphys uterus are asymptomatic, but some present with dyspareunia or dysmenorrhea in the presence of a varying degree of longitudinal vaginal septum. Rarely, genital neoplasms, hematocolpos/hematometrocolpos (a collection or retention of blood in the vagina and/or in the uterine cavity), and renal anomalies are reported in association with didelphys uterus. Despite some of these complications, there are many cases of women with a didelphys uterus that did not exhibit any reproductive or gestational challenges.

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Sources

Uterine septum ―sourced from Wikipedia licensed under CC BY-SA 3.0
Bicornuate uterus ―sourced from Wikipedia licensed under CC BY-SA 3.0
Uterus didelphys ―sourced from Wikipedia licensed under CC BY-SA 3.0
Vaginal septum ―sourced from Wikipedia licensed under CC BY-SA 3.0
A_system_of_gynecology_(1887)_(14802859803) ―by Internet Archive Book Images licensed under CC BY-SA 3.0
Operative_gynecology_-_(1906)_(14760507606).jpg ―by Internet Archive Book Images licensed under CC BY-SA 3.0
Uterus didelphys ―by Internet Archive Book Images licensed under no known copyright restrictions
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