Uterine Anomaly
A uterine anomaly is a difference in the shape or structure of the uterus present from birth, arising from how the organ formed during fetal development. The uterus develops from two tubes that migrate toward the midline, fuse together, and then dissolve the wall between them to create a single cavity. Interruption at any stage produces a recognisable pattern—a uterus divided by a partition, two separate cavities, a single-sided uterus, or no uterus at all. Many women have one of these without ever knowing, discovering it incidentally or only when investigating recurrent miscarriage or difficulty conceiving. The practical significance varies enormously by type: some carry no consequences at all, while others meaningfully affect pregnancy and are worth identifying.
What is it?
The uterus, fallopian tubes, cervix, and upper vagina all develop from a pair of structures called the Müllerian ducts, which appear early in fetal life on either side of the developing abdomen.
Three sequential steps produce a normal uterus. The ducts must form properly on both sides. They must then migrate toward the midline and fuse together in their lower portions, while their upper portions remain separate to become the fallopian tubes. Finally, the wall between the fused ducts must dissolve, converting two adjacent channels into a single cavity.
Almost every uterine anomaly can be understood as a failure at one of these three stages, and this framework makes the otherwise confusing terminology straightforward.
Failure of formation produces absence or underdevelopment. If both ducts fail, the uterus does not develop—this is Müllerian agenesis, also called MRKH syndrome, in which the uterus and upper vagina are absent while the ovaries are present and functioning normally. If one duct fails, the result is a unicornuate uterus: a single, smaller, banana-shaped uterus formed from one side only, sometimes with a small rudimentary horn attached on the other.
Failure of fusion produces two separate cavities. Complete failure gives uterus didelphys—two entirely separate uteri, each with its own cervix, often with a vaginal septum dividing the vagina as well. Partial failure gives a bicornuate uterus, in which the lower portion is fused but the upper portion remains divided, producing a heart-shaped organ with an indented outer contour and two horns.
Failure of resorption produces a division within an otherwise normally shaped uterus. This is the septate uterus: the outside looks normal, but a wall of tissue extends down into the cavity, partially or completely dividing it. An arcuate uterus represents the mildest version, with only a slight indentation at the top of the cavity, and is generally regarded as a normal variant rather than an anomaly.
One distinction is more important than any other in this field: **septate versus bicornuate**. Both produce a divided cavity and can look identical on tests that show only the inside of the uterus. The difference lies in the outer contour—a septate uterus has a smooth, normal outer surface, while a bicornuate uterus is indented from outside. This matters because a septum can be divided through a straightforward hysteroscopic procedure, while a bicornuate uterus cannot be corrected without major reconstructive surgery that is rarely justified. Misclassifying one as the other risks either an unnecessary operation or a missed treatable cause of miscarriage, and it is the main reason imaging that shows both the cavity and the outer contour is required.
Several classification systems exist, which contributes to confusion when women compare information from different sources. Older systems differ from the more recent ones used in European and international guidance, and thresholds for what counts as a septum versus a normal variation have changed. A woman told she has an arcuate uterus under one system might be described differently under another, and this is a reasonable thing to ask a clinician to clarify.
The association with kidney abnormalities is practically important. Because the reproductive and urinary systems develop in close proximity from related tissue, a problem affecting one commonly affects the other. Kidney anomalies—most often absence of one kidney, a pelvic or horseshoe kidney, or duplication—are found in a substantial proportion of women with uterine anomalies, and the association is strongest with unicornuate and didelphys uteri and with obstructed anomalies. Imaging of the kidneys is therefore recommended whenever a uterine anomaly is identified.
An important specific combination is the obstructed hemivagina with ipsilateral renal agenesis, sometimes called OHVIRA or Herlyn-Werner-Wunderlich syndrome, in which a didelphys or septate uterus is accompanied by a blocked vaginal canal on one side and absence of the kidney on that same side. Menstrual blood accumulates behind the obstruction, producing progressively worsening cyclical pain in an adolescent who is nonetheless having apparently normal periods from the unobstructed side. It is a classic cause of severe period pain in a young girl and is frequently diagnosed late.
Most uterine anomalies cause no symptoms and many women never learn they have one.
Where they do cause problems, the effects fall into recognisable groups.
Reproductive effects are the most common reason anomalies come to attention. Recurrent miscarriage, particularly in the first and second trimesters, is the classic presentation, and a septate uterus carries the highest risk—thought to reflect implantation on the poorly vascularised septum. Preterm birth, abnormal fetal position including breech and transverse lie, restricted fetal growth, and higher caesarean rates all occur with varying frequency depending on type. Most anomalies affect the ability to carry a pregnancy rather than to conceive, and fertility itself is often normal.
Obstructive effects occur where menstrual blood cannot escape. A non-communicating rudimentary horn, an obstructed hemivagina, or a transverse vaginal septum causes blood to accumulate, producing severe, progressively worsening cyclical pelvic pain beginning around the time periods start. This can be mistaken for ordinary period pain or for endometriosis, and delay is common. Accumulated blood can also promote endometriosis.
Absent periods despite normal breast and pubic hair development suggests either absence of the uterus, as in Müllerian agenesis, or complete obstruction of the outflow tract, and warrants prompt assessment in an adolescent.
Painful periods, pelvic pain, and difficulty with tampons or intercourse can occur, particularly with vaginal septa.
An important pregnancy-specific risk deserves mention. A pregnancy implanting in a rudimentary horn that does not communicate with the main uterus can grow until the horn ruptures, typically in the second trimester, causing catastrophic internal bleeding. This is uncommon but is one of the more dangerous consequences of uterine anomalies and is a reason rudimentary horns are often removed once identified.
Diagnosis depends on imaging that shows both the cavity and the external shape of the uterus.
Three-dimensional transvaginal ultrasound has become the preferred first-line test. It reconstructs the uterus in the plane needed to assess both the cavity and the outer contour simultaneously, and in experienced hands it is highly accurate—accurate enough that it has largely replaced more invasive alternatives for making the crucial septate-versus-bicornuate distinction.
MRI provides comprehensive anatomical assessment and is used where ultrasound is inconclusive, where anatomy is complex or obstructed, before surgery, and in adolescents where transvaginal scanning is not appropriate. It also images the kidneys in the same examination.
Two-dimensional ultrasound and hysterosalpingography demonstrate the cavity but not the outer contour. Hysterosalpingography, which involves injecting contrast through the cervix and taking X-rays, remains useful for assessing whether the fallopian tubes are open during fertility investigation, but on its own it cannot distinguish a septate from a bicornuate uterus—both show a divided cavity. Historically this limitation led to unnecessary operations, and it is the reason a finding on hysterosalpingography is followed by three-dimensional ultrasound or MRI rather than acted upon directly.
Saline infusion sonohysterography outlines the cavity with fluid during ultrasound and improves assessment of a septum’s extent.
Hysteroscopy visualises the cavity directly and is used both to assess and to treat a septum, frequently combined with laparoscopy in complex cases so that the outer contour can be inspected at the same time.
Kidney imaging is recommended in all cases, usually by ultrasound.
Important to Know
The essential message is that most uterine anomalies require no treatment, and that identification matters mainly for women with reproductive difficulties or obstruction. Care is typically coordinated by gynaecologists, with reproductive medicine, paediatric and adolescent gynaecology, and specialist surgical input as relevant.
Finding an anomaly incidentally, in a woman with no symptoms and no reproductive problems, generally requires nothing more than an explanation and kidney imaging. Many women with an arcuate or mildly septate uterus have entirely normal pregnancies, and the finding should not be presented as a problem in the absence of evidence that it is causing one.
The septate uterus is the anomaly most worth identifying, because it is the one that can be corrected. Hysteroscopic division of the septum is a short day-case procedure performed through the cervix without any abdominal incision, with rapid recovery. Observational studies have consistently reported improved live birth rates and reduced miscarriage after the procedure in women with a history of recurrent loss.
An honest caveat belongs here. Randomised evidence has been less conclusive than the observational literature, with at least one randomised trial finding no clear improvement in reproductive outcomes after septum division. The procedure is therefore generally reserved for women with recurrent miscarriage or established reproductive difficulty rather than offered routinely to any woman found to have a septum, and the uncertainty is worth discussing directly rather than assuming benefit.
Bicornuate and didelphys uteri are rarely operated on. Reconstructive surgery to unify a divided uterus is a major abdominal procedure with significant recovery, a scarred uterus that usually necessitates caesarean delivery, and limited evidence of benefit. Most women with these configurations are managed expectantly, with additional monitoring during pregnancy.
Unicornuate uterus is managed similarly, with pregnancies monitored for preterm birth and growth restriction. Where a rudimentary horn is present and does not communicate with the main cavity, removal is generally recommended before pregnancy, because of the risk of a pregnancy implanting there and causing rupture.
Obstructive anomalies require surgical relief, and in adolescents this is often urgent, since accumulating blood causes increasing pain and can damage the reproductive tract. Relieving an obstructed hemivagina or resecting a transverse vaginal septum typically resolves symptoms and preserves function.
Müllerian agenesis requires a different kind of care. Women have functioning ovaries and normal hormonal development, so puberty proceeds normally and biological children are possible through surrogacy using their own eggs. Uterine transplantation has moved from experimental to available in a small number of specialist centres and has resulted in live births. Vaginal length can be created without surgery through graduated dilator use, which is the recommended first-line approach and is effective for most women, with surgical creation reserved for those in whom it fails. Psychological support is an important part of care, since the diagnosis is usually made in adolescence and has significant implications.
Pregnancy management with a known anomaly generally means additional surveillance rather than intervention. Monitoring for preterm birth, checking fetal position, assessing growth, and planning delivery accordingly are typical. Cervical length surveillance is used in some settings. Caesarean rates are higher, partly because of abnormal fetal position rather than the anomaly itself requiring it.
Fertility is often normal. A common misconception is that a uterine anomaly prevents conception, when in most cases conception occurs normally and the difficulty, if any, lies in maintaining the pregnancy. Women should not assume they cannot conceive and should use contraception accordingly if pregnancy is not desired.
Kidney assessment should be arranged whenever an anomaly is identified, since a missing or abnormal kidney has implications for medication safety, blood pressure, and future health that extend well beyond reproductive care.
Genetic and familial considerations are limited. Most Müllerian anomalies occur sporadically without an identified genetic cause, though there is a modest familial tendency, and relatives with relevant symptoms may reasonably be assessed. They are not generally inherited in a predictable pattern.
Care is coordinated by gynaecology, with reproductive medicine, adolescent gynaecology, urology, and psychology as needed, and referral to a centre with specific experience is worthwhile for complex or obstructed anatomy. Imaging findings are interpreted alongside symptoms, reproductive history, and plans rather than in isolation.
Patient education plays an important role. Understanding which type of anomaly is present and what it does and does not mean, that most require no treatment, that fertility is often unaffected even where miscarriage risk is raised, that the septate-bicornuate distinction determines whether surgery is even possible, and that kidney imaging is part of the assessment all contribute to appropriate care and considerably less anxiety.
Red flag symptoms include severe, progressively worsening cyclical pelvic pain in an adolescent, particularly beginning around the time periods start, which may indicate an obstructed anomaly; absent periods by the age of 15 despite normal breast development and pubic hair; a palpable lower abdominal mass with cyclical pain; sudden severe abdominal pain with dizziness or fainting in early pregnancy, which may indicate rupture of a pregnancy in a rudimentary horn and is a life-threatening emergency; heavy bleeding or severe pain in pregnancy; and difficulty passing urine with pelvic pain. These warrant prompt medical evaluation, urgently where pregnancy or obstruction is involved.