What Is Unicornuate Uterus

  • Anna Mizerska Masters in Global Health and Biomedical Engineer, Norwegian University of Science and Technology (NTNU), Norway
  • Isobel Cronshaw BEng in Biomedical Systems Engineering, University of Warwick

A unicornuate uterus, a single-horned uterus, or a uterus with one horn, is a condition characterised by the presence of only half of a uterus. Individuals with this condition have one functional fallopian tube instead of the usual two, and their uterine cavity (the inside of their uterus) is smaller. This is a congenital uterine anomaly, meaning it is present from birth, and the body naturally reabsorbs the non-functional half of the uterus.

In individuals assigned female at birth, a usual uterus features two connecting fallopian tubes, with the hollow cavity serving as the space where a baby develops, resembling an inverted pear. The fallopian tubes, akin to horns, extend from the top on either side. A unicornuate uterus deviates from this norm, presenting a single-horned structure.

Approximately 75% of those with a unicornuate uterus may have a remnant called a rudimentary horn.1 This is caused by the residual uterine tissue that was absorbed still being connected to the unicornuate uterus. Furthermore, the rudimentary horn may or may not have a functional endometrial lining (the lining of the uterus which thickens for pregnancy and sheds to produce a period) or cavity.

Individuals with a unicornuate uterus may face challenges such as miscarriages or preterm deliveries. When a rudimentary horn is associated with a unicornuate uterus, pelvic pain can also be a potential concern. Understanding and addressing the specific characteristics of the unicornate uterus is crucial for informed reproductive health management.1


The symptoms of a unicornuate uterus can vary, and some individuals may be unaware of the condition until they become pregnant or undergo fertility assessments. In cases where the functioning rudimentary horn is connected to the uterus, individuals may remain asymptomatic throughout their lives. This is because blood can drain from the horn and exit through the vagina.

However, if the rudimentary horn is not connected to the uterus and contains a functional endometrial lining, symptoms may manifest due to the backup of menstrual fluid. Signs of an obstructed rudimentary horn can include:

  1. Pain during Menstruation: Women may experience pain during their menstrual periods.
  2. Frequent Pelvic Pain: Chronic pelvic pain can be a symptom, particularly if there is an obstruction in the rudimentary horn.
  3. Haematometra: This refers to the retention of blood in the uterus, leading to potential discomfort and pain.


It is a congenital abnormality that occurs during fetal development. Specifically, it happens when the two Mullerian ducts (structures which form the uterus and fallopian tubes in an embryo) fail to fuse together as they normally would. One Mullerian duct develops into the smaller unicornuate uterus, while the other duct is reabsorbed by the body. In a typical uterus, these ducts merge to form the complete structure. The precise reasons for the failure of fusion in some cases are not fully understood by healthcare providers.1

Diagnosis & tests

Diagnosing a unicornuate uterus typically involves a comprehensive approach, starting with a physical examination and discussion of your medical history, including a pelvic exam. While it's not often detected during routine gynaecological exams, symptoms such as recurrent miscarriages, fertility challenges, or painful periods may prompt further investigation.

Healthcare providers use various imaging tools to diagnose a unicornuate uterus, including:

  1. Ultrasound: Both 2D and 3D ultrasound imaging can provide detailed views of the uterus, helping identify its shape and any potential obstructions.
  2. MRI (Magnetic Resonance Imaging): MRI offers high-resolution images that can reveal the size, shape, and structure of the uterus and any associated rudimentary horn.
  3. Hysterosalpingogram (HSG): This diagnostic procedure involves injecting a contrast dye into the uterus and fallopian tubes to make them visible on X-rays, helping to identify any abnormalities.

In the diagnostic process, healthcare providers consider different types of rudimentary horns associated with a unicornuate uterus:

  • No Rudimentary Horn: The most common variation, where there is no second horn or remnants of a second fallopian tube, typically causing no painful symptoms.
  • Rudimentary Horn with No Cavity: In this type, the second horn is present but lacks a lining, resulting in no collection of blood and usually causing no painful symptoms.
  • Communicating Rudimentary Horn: This variation involves a connected horn containing endometrium (endometrial lining), allowing blood and fluid to move from the horn down to the uterus and out of the vagina.
  • Noncommunicating Rudimentary Horn: This type features a horn with an endometrium that is not connected to the rest of the uterus, leading to complications such as pelvic pain, haematometra (retaining blood in the horn), and an increased risk of pregnancy complications.

The distribution of these variations among individuals with a unicornuate uterus is approximately 35% with no rudimentary horn, 33% with a rudimentary horn with no cavity, 22% with a noncommunicating rudimentary horn, and 10% with a communicating rudimentary horn.1

In summary, imaging tools such as 3D ultrasound, MRI, HSG, and sometimes hysteroscopy in conjunction with laparoscopy are crucial for accurately diagnosing a unicornuate uterus and assessing associated structures and complications.1

Management & treatment

The approach to treating a unicornuate uterus depends on factors such as the presence of a rudimentary horn, its connection to the uterus, and whether there is endometrium inside the horn. Surgical intervention is not typically recommended unless there are severe symptoms, such as significant pain or the development of a mass within a non-communicating rudimentary horn with an endometrial cavity. This type of rudimentary horn poses a high risk of health complications, particularly during pregnancy, and can lead to pelvic pain due to trapped menstrual blood.

If there is no rudimentary horn or if the rudimentary horn lacks functioning endometrial tissue, treatment may not be necessary.

The goal of surgery would be to remove a functioning rudimentary horn. This can help alleviate pelvic pain and eliminate the risk of a pregnancy growing inside the horn, which could be life-threatening.

 It's important to note that surgery is not a recommended solution for altering the shape or appearance of a unicornuate uterus, as these structural characteristics cannot be changed. The focus is on addressing specific complications, such as a functioning non-communicating horn, to improve overall health and reduce risks associated with pregnancy.

Complications of treating a unicornuate uterus are generally associated with the surgical removal of a functioning rudimentary horn. As with any surgery, there are inherent risks, and the decision to proceed with surgery should be carefully considered in consultation with healthcare professionals.1


How can I prevent a unicornuate uterus?

A unicornuate uterus is a congenital anomaly that takes shape during foetal development. It occurs when the two Mullerian ducts, structures in the developing embryo responsible for forming the female reproductive organs, fail to fuse as part of the natural developmental process. One Mullerian duct gives rise to the smaller unicornuate uterus, while the other undergoes absorption by the body.

Typically, individuals are unaware of having a unicornuate uterus until they embark on pregnancy or fertility attempts. It is crucial to note that there are no preventive measures that an individual or their birthing parent could have taken to avoid the development of a unicornuate uterus. This condition is intrinsic to the natural course of embryonic development.1

How will having an abnormal womb affect my pregnancy?

When your womb deviates slightly from the norm, your chances of experiencing a straightforward pregnancy are as likely as any other individual assigned female at birth. The outcome depends on the type and extent of the abnormality, and the number of pregnancies you've had may also play a role.

It's important to note that various abnormalities, even if minor, elevate the risk of premature labour. Unfortunately, some abnormalities increase the likelihood of early or late miscarriage.

Throughout pregnancy, the limited space within your womb may result in your baby being small for their gestational age. Additionally, the stretching capacity of your womb may reach its limit, potentially triggering early labour.

Having a uterine abnormality may also increase the likelihood of a weak cervix, which might not be robust enough to retain your baby in the womb. A prematurely opening cervix can lead to premature labour or late miscarriage. Fortunately, there are treatments available for a weak cervix, and your obstetrician will discuss these options with you.2

What are the pregnancy complications of a unicornuate uterus?

Pregnant individuals with a unicornuate uterus face heightened risks, including:

  1. Miscarriage
  2. Stillbirth
  3. Preterm Birth
  4. Malpresentation: The baby is in a breech or transverse position in the uterus.
  5. Ectopic Pregnancy: Pregnancy occurring outside the uterus.
  6. Heavy Vaginal Bleeding 
  7. Placental Problems: Issues like placenta previa or placental abruption.

If pregnancy occurs in the rudimentary horn, it can pose a potentially life-threatening situation. In non-communicating horns, there's a heightened risk of uterine rupture due to the limited space.

Individuals with any type of unicornuate uterus require close monitoring during pregnancy. This involves more frequent appointments and ultrasounds. Medications may be employed to mitigate the risk of preterm delivery, ensuring comprehensive care for both the individual and the baby.1

How will the unicornuate uterus affect my delivery?

Individuals with a unicornuate uterus are more prone to having a cesarean section (c-section) during childbirth. The restricted space within the uterus often leads to the baby assuming a breech position. In a breech presentation, the baby's feet or bottom is positioned downward in the uterus instead of the preferred head-first position. Given the increased likelihood of breech presentation in a unicornuate uterus, healthcare providers often opt for a c-section to ensure safer delivery for both the mother and the baby.1


Having a unicornate uterus means that an individual only has half a uterus. It occurs when this part of the body does not develop properly when the individual is a foetus, but is often not discovered until the individual is trying to get pregnant. Often the other half of the uterus is absorbed, however, it may be connected to the unicornate uterus by what is called a rudimentary horn, which can lead to pregnancy complications and painful symptoms such as pain during menstruation, frequent pelvic pain, and retention of blood. It can be diagnosed using medical imaging. In serious cases, surgery may be recommended to remove a rudimentary horn.

If you possess a unicornuate uterus, it's common to seek information from your healthcare provider and get some questions answered about your condition, such as:

  1. Is pregnancy possible with my unicornuate uterus?
  2. What are the potential risks of pregnancy with my condition?
  3. Can I expect a healthy outcome for my baby?
  4. What are the health implications linked to a unicornuate uterus?
  5. Is there an associated rudimentary horn with my unicornuate uterus?

Learning that you have a unicornuate uterus can be challenging. It is advisable to have a conversation with your healthcare provider to ensure comprehensive self-care and the minimisation of health risks associated with this condition. It's reassuring to know that individuals with a unicornuate uterus can conceive and have healthy pregnancies.1


  1. Unicornuate Uterus: Causes, Symptoms, Diagnosis & Treatment. Cleveland Clinic [Internet]. [cited 2024 Feb 14]. Available from: https://my.clevelandclinic.org/health/diseases/23302-unicornuate-uterus.
  2. Abnormalities of the uterus in pregnancy. BabyCenter [Internet]. [cited 2024 Feb 14]. Available from: https://www.babycentre.co.uk/a551934/abnormalities-of-the-uterus-in-pregnancy.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Anna Mizerska

Masters in Global Health and Biomedical Engineer
Anna is a highly analytical and insightful professional with progressive experience in providing quality services in fast-paced and high-pressure environments. Over the years she has built up extensive knowledge, expertise and transferable skills that translate into writing reliable medical content and articles.

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