Many text-books on gynecology assert that a double uterus, or the absence of the uterus, is a rare occurrence. This has not been my experience. Although my surgical work is confined entirely to private patients, I have seen half a dozen of these anomalies in the course of a few years, so that I can but wonder why in the large clinics embracing the enormous amount of charity and private surgical work, they should be classed as "extremely rare."
These malformations are caused by developmental defects in the early embryonic stage. The vagina and uterus are both developed by the coalescence of the lower two-thirds of the müllerian ducts, and the absorption of their inner wall. If these ducts fail to unite, or the septum is not absorbed, a deformity results to a more or less extent. If the ducts unite and the septum persists there will be a double
PRINCE EM. REPORTS OF UTERINE MALFORMATIONS. JAMA. 1913;60(3):174–176. doi:10.1001/jama.1913.04340030004004