Unicornuate uterus and rudimentary horn: a plain guide, and the surgical case for doctors
A unicornuate uterus is a womb that formed from only one of its two halves, so it is smaller and banana-shaped. The other half may be missing altogether or left as a small rudimentary horn beside the womb. Many women learn of it only during fertility tests, a pregnancy scan or an operation.
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Most women who read the words unicornuate uterus on a report have never heard of the condition, and it can feel alarming. This guide explains in plain words what it means, why it matters for periods, fertility and pregnancy, and when an operation is advised. The second half is written for doctors and walks through the surgical case shown in the video. It is general information only; your own doctor will explain what your scans mean for you.
What is a unicornuate uterus?
Before birth, the womb forms from two small tubes of tissue, the Müllerian ducts, which grow towards each other and join to make one uterus with a fallopian tube on each side. In a unicornuate uterus, only one of these ducts develops fully. The result is a narrower, banana-shaped womb that leads to one fallopian tube, with one cervix. It belongs to a group of birth differences of the womb called Müllerian, or uterine, anomalies, which also include the septate, the bicornuate and the double uterus. The ovaries form separately, so both ovaries are usually present and work normally.
The rudimentary horn
The half that did not develop fully is often present as a small rudimentary horn attached to the side of the main womb. Doctors describe the horn in two ways:
- Does it have a cavity? Some horns are solid muscle. Others hold a small cavity lined with endometrium, the lining that bleeds each month.
- Does it connect? A communicating horn opens into the main womb; a non-communicating horn does not.
A horn with a lining but no opening is the one that matters most. Its monthly blood has nowhere to go, which can cause cyclical pain, and it is linked with endometriosis. A pregnancy can also settle in the horn, where the thin wall cannot stretch the way a womb does, and this can become an emergency.
How this uterine anomaly is found
A unicornuate uterus can be hard to see on an ordinary two-dimensional ultrasound, and a rudimentary horn can look like a fibroid or a lump beside the ovary. A 3D ultrasound or an MRI shows the outline of the womb and of the horn much more clearly. An X-ray of the womb and tubes shows a single, curved cavity that opens into one tube; read about the HSG tube test. Sometimes, as in the case in the video, the full picture becomes clear only at laparoscopy.
The kidneys and the womb form at the same time, so a kidney is sometimes missing or out of place, usually on the side of the missing half. A simple kidney ultrasound is therefore advised once the anomaly is found.
Unicornuate uterus and pregnancy
Many women with a unicornuate uterus conceive and carry a pregnancy. The smaller womb does bring a higher chance of miscarriage, of early labour, of the baby lying breech and of slower growth of the baby, so pregnancy care is closer than usual: early scans, checks of the length of the cervix, and growth scans later on. Women who have had repeated losses are assessed as set out in our guide to recurrent miscarriage. The shape of the womb is rarely the only reason a couple has not conceived, so the usual fertility tests for both partners still matter.
When is surgery advised?
Treatment is about the horn and its surroundings, not the main womb, which cannot be enlarged. Gynaecology guidelines generally advise removing a rudimentary horn that has a cavity lined with endometrium, even before any symptoms, because of the risk of a pregnancy in the horn and of cyclical pain. A solid horn with no cavity usually needs no operation unless it causes trouble. Fibroids, when they are present as well, bring their own questions; our page on fibroid treatment explains them. Where an operation is needed, it is usually a keyhole operation.
For doctors: the case in the video
The rest of this page is written colleague to colleague. The video's description sets out the case:
- Indication: surgery was planned for an adnexal mass in a woman with infertility. On ultrasound, the mass was thought to be a fibroid, possibly in the broad ligament, and smaller fibroids were also seen.
- Findings at laparoscopy: a unicornuate uterus with a non-communicating rudimentary horn. The horn carried a large fundal fibroid and two smaller fibroids, and the unicornuate uterus itself had multiple fibroids.
- Decision on the table: to remove all the fibroids first, from the main uterus and from the horn, so that the true anatomy could be understood without them. The patient had told the surgeon that her fertility mattered to her.
- Part 2: after the multiple myomectomy, the excision of the rudimentary horn.
In this video, our consultant makes the point that the findings at surgery can differ from the scan, and that the surgeon must be prepared for surprises.
Müllerian anomaly surgery: general technical points
These are general principles from the published literature, not a description of the video:
- Map the anatomy first. Identify the round ligament, the tube and the utero-ovarian ligament on the side of the horn, and the fibrous or muscular band that joins the horn to the unicornuate uterus.
- Know where the ureter is before dividing the pedicles of the horn; it may lie close to the line of excision, and renal anomalies travel with this condition.
- Keep the ovary. The ovary on the side of the horn is usually preserved, and many surgeons remove the tube on that side with the horn, to lower the chance of a later tubal ectopic pregnancy there.
- Protect the main uterus. Divide the connecting band close to the horn, without breaching the myometrium of the unicornuate uterus, and repair any defect in layers.
- Record the repair. Note any cavity entry and the depth of the myometrial repair after a myomectomy, because it guides the plan for a later delivery. The principles of enucleation and closure are in our CME article on laparoscopic myomectomy technique.
Afterwards, counsel the patient that the unicornuate uterus itself is unchanged by the operation, so pregnancy care stays closer than usual, and that the timing of a pregnancy after a multiple myomectomy depends on the depth of the repair.
About this guide
This guide is by the Pai Hospital Team. Pai Hospital is at Vaddem, Vasco-da-Gama, Goa, with its own operating theatre, and it is open 24 hours for pregnancy and gynaecology emergencies. The video is one of our consultant's teaching videos on YouTube; it shows one patient's operation, and every woman's case is different.
This article is for education only and is not personal medical advice; please speak to your own doctor about your situation.
Your questions
Can I get pregnant with a unicornuate uterus?
Yes, many women do. The smaller womb brings a higher chance of miscarriage, early labour and a breech baby, so the pregnancy is watched more closely, with extra scans and checks of the cervix.
Does a rudimentary horn always need to be removed?
No. A horn that has a cavity lined with endometrium is usually removed, because a pregnancy or trapped menstrual blood there can cause serious problems. A solid horn with no cavity often needs no operation.
Can a unicornuate uterus be corrected by surgery?
No. The main womb cannot be enlarged or rebuilt. Surgery deals with a rudimentary horn, with fibroids, or with other problems around the womb.
Why was a kidney scan advised after my uterus scan?
The kidneys and the womb develop at the same time before birth, so a missing or misplaced kidney is more common with this anomaly. A simple ultrasound of the kidneys checks for it.
Is a unicornuate uterus the same as a bicornuate uterus?
No. A bicornuate uterus has two halves that did not fully join, which gives it a heart shape. A unicornuate uterus has only one half that formed fully.
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This page is for general education and is not personal medical advice. Treatment depends on your own examination and reports, so please speak to a doctor about your situation. We do not carry out or offer sex determination of any kind.