In a female fetus, the uterus starts out as two small tubes. As the fetus develops, the tubes normally join to create one larger, hollow organ the uterus. Sometimes, however, the tubes don't join completely. Instead, each one develops into a separate structure. This condition is called double uterus (uterus didelphys).
The cause of double uterus is unknown. This condition may be associated with kidney abnormalities, which suggests that something may influence the development of these related structures before birth. Surgery to unite a double uterus is rarely done although surgery may help you sustain a pregnancy if you have a partial division within your uterus and no other medical explanation for a previous pregnancy loss. Patients with a double uterus may need special attention during pregnancy as premature birth and malpresentation are common.