What Are Congenital Uterine Anomalies?

Congenital uterine anomalies are structural differences in the shape of the uterus that develop before birth, during fetal development.[^1][^2] The word “congenital” means present from birth — these aren’t conditions you develop later in life.

CUAs arise when the Müllerian ducts (the embryonic structures that form the uterus, fallopian tubes, cervix, and upper vagina) don’t develop, fuse, or reabsorb properly during embryonic development, primarily between approximately weeks 6 and 12 of gestation.[^6][^7] The result can be anything from a minor indentation in the uterine wall to a completely divided or absent uterus.

Prevalence estimates (how common CUAs are in a population) vary widely — from under 1% to as high as 38% depending on the study, the population screened, and the diagnostic method used.[^1] A more practical estimate: CUAs affect about 1–4% of the general fertile population, but the rate is significantly higher — around 8.5–12% — in women with infertility or recurrent pregnancy loss.[^3][^4]

Think of it this way: the uterus is built from two tubes that need to come together and merge into one hollow organ. If that merging process stalls at any stage, the final shape is different. Most of the time, the person has no idea.

How Does the Uterus Form Before Birth?

The uterus develops from paired embryonic structures called Müllerian ducts (also known as paramesonephric ducts). This process begins around week 6 of fetal life and proceeds in three overlapping phases.[^6][^7]

The Three Phases of Müllerian Duct Development

1. Initiation and elongation — the ducts begin to form and grow downward alongside the developing kidneys.[^6]

2. Fusion — the two ducts meet in the midline and fuse together, creating a single uterine cavity. The fallopian tubes remain separate at the top.[^6][^7]

3. Septal resorption — the tissue wall (septum) between the two fused ducts dissolves, leaving one continuous cavity.[^6][^7]

A disruption at any of these stages produces a different type of CUA. Complete fusion failure? Two separate uteri (uterus didelphys). If the septum doesn’t resorb, the cavity stays divided — that’s a septate uterus. And if only one duct develops properly, a unicornuate uterus, smaller and asymmetric, with just one functioning tube.[^7]

Key Insight:
Because the Müllerian ducts develop alongside the kidneys (mesonephric system), renal evaluation may be considered, particularly in anomalies such as a unicornuate uterus or when syndromic features are suspected. Renal abnormalities are found in a notable proportion of cases, particularly with unicornuate and didelphys uteri.[^7]

What Are the Main Types of CUAs?

CUAs can be broadly divided into two groups based on the developmental stage at which the problem occurs: unification defects (failure of the ducts to fuse) and canalization defects (failure of the midline septum to dissolve).[^1][^8]

Septate and Subseptate Uterus (Canalization Defects)

The septate uterus is the most common CUA, accounting for roughly 35% of all diagnosed uterine anomalies.[^4] A tissue wall (septum) divides the uterine cavity either partially (subseptate) or completely (septate). The outer contour of the uterus appears normal.[^2][^8]

This matters because the septum may have altered vascularisation and endometrial characteristics, which may contribute to impaired embryo implantation and poorer reproductive outcomes.[^4] An embryo that implants on the septum may not get the blood supply it needs, which is why septum-related pregnancy losses can occur in both the first and second trimesters.[^1] A 2022 meta-analysis of 38 observational studies found that women with a septate uterus had over four times the rate of miscarriage (OR 4.29) compared to women without a septum.[^4] Their live birth rate is also significantly lower (OR 0.25).[^1]

Here’s the catch: a septate uterus is also the CUA with the clearest established treatment option. Hysteroscopic septum resection is a well-established, minimally invasive procedure — more on that below.

Unicornuate Uterus (Unification Defect)

A unicornuate uterus develops when only one Müllerian duct forms properly — the other either fails to develop or remains as a rudimentary horn. The result is a smaller-than-normal, banana-shaped uterus with typically one functioning fallopian tube.[^2][^15]

Women with a unicornuate uterus have a reduced clinical pregnancy rate (OR 0.75) and face increased risks of preterm birth (OR 2.83), malpresentation (the baby lying bottom- or feet-first instead of head-down), and cervical incompetence (when the cervix opens too early in pregnancy).[^1]

Bicornuate Uterus (Unification Defect)

A bicornuate uterus — sometimes called a “heart-shaped uterus” — occurs when the Müllerian ducts fuse incompletely, leaving two separate horns that share a single cervix.[^15] The external contour of the uterus has a visible indentation at the top, which distinguishes it from a septate uterus on imaging.

The Kim et al. (2021) meta-analysis found that a bicornuate uterus was associated with higher rates of first-trimester miscarriage (OR 2.59), preterm birth (OR 3.69), malpresentation (OR 10.87), and cesarean delivery (OR 5.23).[^1]

Uterus Didelphys (Complete Non-Fusion)

When fusion fails entirely, the result is two completely separate uterine cavities, each with its own cervix and sometimes its own vagina.[^2][^15] The didelphys uterus is associated with increased rates of preterm birth (OR 4.93) but is not significantly associated with miscarriage or reduced fertility in pooled analyses.[^1]

Arcuate Uterus

An arcuate uterus has a mild concave indentation at the fundus (the top of the uterus). The mildest CUA — many experts consider it a normal variant rather than a true anomaly.[^1][^8] Most studies show no significant increase in first-trimester miscarriage compared to a normal uterus.[^1]

T-Shaped Uterus and Uterine Agenesis

A T-shaped uterus has a narrow, elongated cavity. It was historically linked to in-utero exposure to diethylstilbestrol (DES) — a synthetic estrogen given to pregnant women, mainly between the 1940s and 1970s, which affected the developing uterus before birth. Because the drug is no longer used, this cause is now rare, and a T-shaped uterus can also occur without any DES exposure.[^8][^15]

In rare cases, the uterus may be completely absent — a condition known as Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome. Women with MRKH have functioning ovaries but no uterus, making pregnancy possible only through surrogacy (where it is legally available) or, in a limited number of centers, uterus transplantation.[^14]

→ Learn more: Female Infertility

How Are CUAs Classified?

Several classification systems exist, and none is universally accepted, which contributes to the wide variation in reported prevalence rates.[^2][^5]

Sources: Akhtar et al. (2025), Grimbizis et al. (2013), and Pfeifer et al. (2021)[^2][^5][^8]

The distinction matters practically. A septate uterus and a bicornuate uterus can look similar on basic 2D ultrasound, but their treatment is completely different — hysteroscopic resection for a septum versus potential abdominal surgery (if any) for a bicornuate uterus. They can even receive different classifications depending on which system the specialist uses, so seeing a clinician who specializes in CUAs matters — it gives you the most accurate diagnosis and, with it, the right treatment plan.[^2][^9]

What Symptoms Do CUAs Cause, and How Are They Diagnosed?

Many women with CUAs have no symptoms at all.[^1][^2] The anomaly is often discovered incidentally during a routine ultrasound, a fertility workup, or after pregnancy complications.

What Symptoms May Occur?

When symptoms do occur, they may include painful menstruation (dysmenorrhea), abnormal uterine bleeding, pain during intercourse, and — in cases of obstructive anomalies — cyclic pelvic pain beginning at menarche.[^1][^2][^9] But the most common “symptom” is a reproductive problem: recurrent miscarriage, preterm birth, or difficulty conceiving.

How Are CUAs Diagnosed?

Accurate diagnosis requires assessing both the internal cavity shape and the external contour of the uterus — a standard 2D ultrasound can miss a lot.[^9]

• Three-dimensional transvaginal ultrasound (3D TVUS) is now widely considered a first-line imaging modality. A 2023 meta-analysis confirmed that 3D ultrasound significantly outperforms standard 2D ultrasound for identifying a septate uterus, with high sensitivity and specificity.[^10] A 2024 retrospective cohort study found that 3D TVUS detected CUAs in 8–19% of women with unexplained recurrent pregnancy loss — anomalies that had been missed on prior assessments.[^11]

• Magnetic resonance imaging (MRI) is particularly valuable in complex cases, especially when surgery is being planned or when ultrasound results are inconclusive.[^2][^9] It provides detailed soft tissue contrast and can clearly distinguish a septate uterus from a bicornuate one.

• Hysteroscopy and laparoscopy were historically the combined gold standard, but their invasive nature has now reserved them for cases where intervention is also planned.[^9]

Important:
A normal 2D ultrasound may not exclude some CUAs, particularly subtle cavity anomalies such as a septum. If you have unexplained recurrent miscarriages or infertility, you can ask your specialist whether a 3D ultrasound or an MRI would be appropriate to get a more detailed view of your uterine shape and structure.[^2][^9][^10]

How Do CUAs Affect Fertility and Pregnancy?

The impact varies substantially by anomaly type.[^12] But the overall picture is clear: CUAs are associated with lower live birth rates, higher miscarriage rates, and increased obstetric complications.[^1]

Source: Kim et al. (2021). OR = odds ratio vs. normal uterus; NS = not statistically significant.[^1]

Odds ratios describe relative — not absolute — risk and do not predict an individual patient’s outcome.

What’s reassuring, though, is that most pregnancies in women with CUAs do result in a live birth — the complication rates are higher, but a successful outcome is still the most likely scenario.[^13] The key is knowing the anomaly is there, so the pregnancy can be monitored appropriately.

Bottom Line:
The type of CUA matters. Septate uteri carry the highest miscarriage risk but are also the most treatable. Unification defects (unicornuate, bicornuate, didelphys) primarily affect pregnancy and delivery in the later stages.[^1][^4]

What Are the Treatment Options?

Treatment depends entirely on the type of anomaly, the severity of symptoms, and your reproductive goals. Not every CUA requires intervention.[^2]

How Does Hysteroscopic Septum Resection Work?

For septate and subseptate uteri, hysteroscopic metroplasty is the primary treatment. This minimally invasive procedure uses a camera-equipped instrument inserted through the cervix to cut or vaporize the septum, restoring a single uterine cavity.[^2][^4]

The data supporting this procedure is largely observational. In observational studies of women with recurrent miscarriage or infertility, substantially higher live birth rates and lower miscarriage rates have been reported following septum resection.[^4] But these findings should be interpreted with caution: the study designs can’t clearly separate the effect of surgery from natural variation in outcomes, or other contributing factors. A separate meta-analysis by Carrera et al. (2022) also reported that hysteroscopic metroplasty reduced the risk of miscarriage.[^16]

Complication rates are low — 1.5–1.8% in the Noventa meta-analysis — and modern instruments have made the procedure even safer.[^4]

That said, the evidence isn’t without its share of debate. One randomized trial (the TRUST trial, 2021) found no significant improvement from septum resection, but it has been interpreted cautiously because of methodological limitations — its small sample size (68 women), mixed patient populations, and other methodological concerns.[^4] Current guidelines continue to recommend metroplasty after individualized evaluation for women with a septate uterus and a history of recurrent miscarriage or infertility.[^2][^17]

How Are Unification Defects Managed?

For unicornuate, bicornuate, and didelphys uteri, there is no standard surgical correction that improves reproductive outcomes.[^2] The historical Strassman metroplasty (abdominal surgery to unify a bicornuate uterus) is rarely performed today due to limited evidence and the risks associated with uterine surgery.

Management is primarily close monitoring during pregnancy: cervical length assessment, early detection of preterm labor, and planned delivery strategies. Cervical cerclage may be considered in selected cases, particularly with unicornuate uteri.[^1][^2]

When Is Assisted Reproduction Needed?

When CUAs contribute to infertility — either directly or alongside other factors — assisted reproductive technology (ART) may be necessary. A 2024 systematic review by Fedele et al. found that both septate and unicornuate uteri were associated with reduced IVF success rates compared to women with a normal uterus.[^14]

For women with septate uteri, septum resection before in vitro fertilization (IVF) may be considered, particularly in selected patients, after specialist evaluation.[^2][^14] For unicornuate and bicornuate uteri, single embryo transfer is preferred. This is consistent with broader contemporary IVF practice, and it’s especially relevant when uterine capacity may be reduced, since it avoids the added risks of a multiple pregnancy in a smaller cavity.[^14]

For women with MRKH syndrome (absent uterus), surrogacy (where legally available) remains the primary path to genetic parenthood, though uterus transplantation is emerging as an option at specialized centers.[^14]

→ Treatment option: In Vitro Fertilization (IVF)

→ Learn more: Uterine Fibroids, Myomas and Uterine Anomalies

So, What Should You Do Now?

If you suspect a CUA or have been diagnosed with one, here’s a practical roadmap.

Step 1: Get the Right Diagnosis

Standard 2D ultrasound may not be sufficient for definitive classification. 3D transvaginal ultrasound is often preferred for detailed classification of congenital uterine anomalies, while MRI may be helpful in selected or complex cases to determine the type and severity of the anomaly. Correct classification is essential for treatment planning.

Step 2: See a Specialist in Reproductive Anatomy

Because diagnosis and management can be nuanced, consulting a clinician experienced in congenital uterine anomalies may be helpful — ideally, one affiliated with a fertility center that performs hysteroscopic procedures.

Step 3: Check for Associated Anomalies

Because the uterus and kidneys develop from related embryonic structures, kidney anomalies are sometimes present alongside uterine ones. You can ask your specialist whether a renal (kidney) ultrasound is appropriate in your case — particularly with anomalies such as a unicornuate uterus — so that any associated finding is identified early.

Step 4: Discuss Treatment Options Based on Your Goals

If you have a septate uterus and a history of miscarriage, hysteroscopic septum resection is the standard recommendation. For other types, discuss monitoring strategies and whether assisted reproduction may be beneficial for your specific situation.

Step 5: Compare Clinics With Relevant Expertise

If IVF or surgical intervention is recommended, compare clinics that have demonstrated experience managing pregnancies with CUAs. Look for specialists who routinely perform 3D ultrasound, hysteroscopy, and high-risk obstetric monitoring.

→ Compare fertility clinics worldwide: MedicalNavigator.com/fertility-clinics

Too Long, Didn’t Read

• CUAs are structural uterine differences present from birth, affecting 1–4% of women.

• The septate uterus is the most common type and carries the highest miscarriage risk (OR 4.29).

• CUAs are often asymptomatic and are frequently found during fertility investigations or incidentally on imaging.

• 3D ultrasound or MRI is often needed for accurate diagnosis, because standard 2D scans can miss the anomaly.

• Hysteroscopic metroplasty may improve outcomes in appropriately selected patients with a septate uterus, with a complication rate of 1.5–1.8%.

• Kidney anomalies can occur alongside CUAs because of shared embryonic origins, so renal imaging may be considered.

References