Pregnancy in a rudimentary horn refers to the implantation and development of a fertilized ovum within a rudimentary uterine horn, most frequently observed in primigravidas. A rudimentary uterine horn is a congenital uterine malformation resulting from an abnormality during the embryonic fusion of the Müllerian ducts, leading to incomplete development of one side of the ducts. This condition is characterized by the presence of a smaller uterus in addition to the primary uterus, with the cavity of the smaller uterus sometimes showing an endometrial stripe. The rudimentary uterine horn often lacks communication with the better-developed uterine cavity on the opposite side.
Pregnancy in a rudimentary horn can occur through two mechanisms:
- Sperm reaches the contralateral fallopian tube, traverses externally, enters the fallopian tube on the affected side, fertilizes the ovum, and the resulting zygote implants in the rudimentary horn.
- A fertilized ovum from the contralateral fallopian tube traverses externally and migrates into the fallopian tube on the affected side, subsequently implanting and developing in the rudimentary horn.
The myometrium of the rudimentary horn is often underdeveloped and cannot sustain fetal growth. In most cases, complete or incomplete rupture of the uterine myometrium occurs between 14 to 20 weeks of pregnancy, resulting in severe internal bleeding. The clinical presentation is similar to the rupture of a tubal interstitial pregnancy. Rarely, pregnancy may reach full term; in such cases, uterine contractions may occur during labor. However, vaginal delivery is impossible, and fetal demise commonly occurs shortly after the onset of labor.
After a definitive diagnosis of pregnancy in a rudimentary horn, timely surgical intervention is necessary. This involves the removal of the rudimentary horn. If the fetus is viable, a cesarean section is performed prior to removing the rudimentary horn.