What Are Uterine Abnormalities? Types and Symptoms

Uterine abnormalities are structural differences in the uterus that fall into two broad camps: those you are born with (congenital) and those that develop later in life (acquired). Congenital forms arise when the paired tubes that build the uterus during fetal development do not fuse or reshape as expected, while acquired forms include growths like fibroids and polyps or scarring from surgery. Some cause no symptoms at all and are discovered only by accident during imaging for something else; others produce painful periods, heavy bleeding, recurrent miscarriage, or difficulty getting pregnant.

How the Uterus Forms and Where Things Can Go Wrong

During fetal development, two structures called the müllerian ducts normally fuse together and then partially resorb to create a single uterine cavity, along with the fallopian tubes, cervix, and upper portion of the vagina.¹ When any step in that sequence stalls, the resulting uterus can end up with a wall down the middle, two separate horns, only one functional half, or in rare cases no uterus at all. The specific shape depends on exactly where in the process the disruption occurred, which is why congenital uterine anomalies range from barely noticeable to profoundly life-altering.

A modern classification system groups these anomalies by their anatomy rather than by the embryological step that went wrong. The system adopted by European reproductive-medicine societies assigns categories from U0 (a normal uterus) through U5 (an absent or severely underdeveloped uterus), with a U6 category reserved for cases that do not fit neatly elsewhere.² In clinical practice, though, most people encounter these conditions under their traditional names: septate, bicornuate, didelphys, unicornuate, and so on.

Congenital Types

Septate Uterus

A septate uterus looks normal on the outside but has a wall of tissue, called a septum, dividing part or all of the interior cavity. This is one of the more common congenital anomalies and historically one of the most studied because of its link to pregnancy loss. The septum is not just a flimsy curtain: imaging and tissue studies consistently show that the septum contains muscle and has its own blood supply, covered by a lining that differs in composition from the normal uterine wall.³ Research comparing women with recurrent pregnancy loss to those with unexplained infertility found that the septa in the pregnancy-loss group were more heavily vascularized and contained more muscular tissue, suggesting the septum’s composition may influence how a pregnancy implants and whether it survives.⁴

Bicornuate Uterus

A bicornuate uterus has two distinct horn-shaped cavities that typically share a single cervix and vagina. The outer surface of the uterus shows a visible cleft at the top, unlike the septate uterus, which looks smooth externally. Most women with this shape have functioning ovaries and can conceive, but maintaining a pregnancy carries higher risk because each horn offers a smaller space for a growing fetus.⁵ Complications such as preterm delivery and malpresentation (the baby not being head-down) are more frequent with this anatomy.

Uterus Didelphys

When the müllerian ducts fail to fuse at all, the result is a double uterus: two entirely separate uterine horns, each with its own cervix, and often a longitudinal wall dividing the vagina as well. Many women with uterus didelphys have no idea anything is unusual; the condition is frequently asymptomatic, though some experience painful intercourse or painful periods.⁶ Pregnancy is possible in either horn, and the outcomes are surprisingly variable, ranging from uncomplicated deliveries to significant preterm birth risk.

Unicornuate Uterus

A unicornuate uterus forms when only one of the two müllerian ducts develops fully, producing a smaller, banana-shaped uterus tilted to one side. In many cases, a small remnant of the other duct exists as a rudimentary horn that may or may not connect to the main cavity. That remnant can become a clinical problem: if it contains functioning endometrial tissue but has no outlet, menstrual blood builds up and causes worsening pelvic pain, especially around periods.⁷ The most common complaints associated with a unicornuate uterus and a non-communicating rudimentary horn include painful periods, infertility, recurrent miscarriage, and chronic pelvic pain. Pregnancies that do occur carry elevated risks of fetal growth restriction and preterm labor.⁸

Absent or Severely Underdeveloped Uterus (MRKH Syndrome)

At the most extreme end, the uterus and upper vagina may never form at all. This condition, known as Mayer-Rokitansky-Küster-Hauser syndrome, typically comes to attention when a teenager has normal external development and normal ovaries but never starts menstruating. The genetic basis remains largely unknown, though research using whole-exome sequencing has narrowed the field to a handful of candidate genes that appear to play a role.⁹ MRKH is often accompanied by kidney, skeletal, cardiac, or hearing abnormalities, which underscores how interconnected the development of these organ systems is during early fetal life.

Acquired Uterine Abnormalities

Not every structural problem with the uterus is present from birth. Several conditions develop during adult life, and these are far more common than congenital anomalies.

Fibroids

Uterine fibroids are benign growths of smooth muscle within the uterine wall. They are extraordinarily common, and their symptoms depend on where in the wall they sit. Imaging guidelines now recommend describing fibroids using a standardized system that maps their relationship to the inner lining, the muscular wall, and the outer surface of the uterus, because that location largely determines whether a fibroid causes heavy bleeding, pressure symptoms, pain, or no trouble at all.¹⁰ Those that bulge into the uterine cavity are the ones most likely to disrupt menstrual bleeding and interfere with implantation. Those pressing outward can cause pelvic pressure, urinary frequency, or back pain. Fibroids that sit entirely within the wall may produce cyclical pain from the pressure they exert on surrounding tissue.¹¹

Endometrial Polyps

Endometrial polyps are overgrowths of the uterine lining that protrude into the cavity. They are benign and affect both women of reproductive age and those who are postmenopausal. Heavy menstrual bleeding is the hallmark symptom when polyps are symptomatic, though in many women they cause no trouble and may even shrink on their own. When they do cause problems, they can be removed during a hysteroscopy, a procedure that is both safe and effective.¹²

Adenomyosis

Adenomyosis occurs when tissue that normally lines the inside of the uterus grows into the muscular wall itself. The misplaced tissue still responds to hormonal cycles, swelling and bleeding within the muscle. The result is a uterus that contracts more forcefully and more often than normal, because the affected muscle develops an increased sensitivity to the hormones that trigger contractions.¹³ On top of that, the affected areas develop extra nerve fibers, meaning even small stimuli can register as disproportionate pain. The classic symptoms are painful periods, chronic pelvic pain, abnormal bleeding, and difficulty conceiving.

Asherman Syndrome

Asherman syndrome is scarring inside the uterine cavity, usually following a surgical procedure performed on a pregnant or recently pregnant uterus, such as a dilation and curettage after miscarriage. The scar tissue (adhesions) can partially or completely block the cavity, producing a triad of symptoms: pain, menstrual disturbances that can range from lighter periods to no periods at all, and infertility.¹⁴ Management remains a contested area, with no clear consensus on the best approach, though hysteroscopic adhesiolysis (breaking up the scar tissue under direct visualization) is the most widely used technique.¹⁵

The Symptom Overlap Problem

One reason uterine abnormalities often go undiagnosed for years is that their symptoms are nonspecific. Heavy menstrual bleeding, for example, can arise from fibroids, polyps, adenomyosis, a septate uterus, or hormonal imbalances that have nothing to do with the uterine structure at all.¹⁶ Painful periods overlap across nearly every condition listed here. Chronic pelvic pain is similarly multifactorial and can involve the bladder and bowel as well: animal research has shown that uterine or pelvic pathology can amplify pain signals in neighboring organ systems through shared nerve pathways, which helps explain why pelvic pain conditions so often cluster together.¹⁷

The practical takeaway is that symptoms alone rarely point to a specific diagnosis. Someone with worsening period pain and heavier bleeding could have adenomyosis, a submucosal fibroid, a polyp, or a congenital anomaly that was never picked up. Imaging is almost always needed to sort things out.

How These Conditions Are Diagnosed

Standard two-dimensional ultrasound is usually the first step, but it misses a lot. Three-dimensional transvaginal ultrasound and MRI both do a much better job of distinguishing, say, a septate uterus from a bicornuate one, a distinction that matters for treatment planning. Studies comparing 3D ultrasound with MRI have found very good agreement between the two techniques for classifying müllerian anomalies.¹⁸ That said, for evaluating the uterine cavity itself, particularly for polyps and adhesions, hysteroscopy (inserting a thin camera through the cervix) remains the preferred method because it allows both diagnosis and treatment in the same session.¹⁹

When a congenital uterine anomaly is identified, imaging the kidneys and urinary tract is a standard next step. The müllerian ducts and the structures that build the urinary system develop side by side in the embryo, so when one goes wrong the other often does too. Uterus didelphys, for instance, is associated with renal anomalies like a missing kidney or a duplicated collecting system.²⁰ The link between kidney and uterine development is well-established across many types of müllerian anomalies, not just didelphys.²¹ Recent genetic work has even identified specific gene variants that can simultaneously cause kidney, uterine, and vertebral defects, reinforcing the idea that these are developmentally linked rather than coincidental.²²

Effects on Pregnancy

The reproductive impact of congenital uterine anomalies is real but varies enormously depending on the specific type and its severity.²³ A large meta-analysis found that the overall risk of preterm delivery was roughly four times higher in women with congenital uterine anomalies compared to those with a normal uterus. But the risk was not evenly distributed. Bicornuate and unicornuate uterine shapes carried some of the highest adjusted risks, while the septate uterus, after statistical adjustment, did not show a significant increase in preterm birth.²⁴ That finding is worth highlighting because the septate uterus is the anomaly most commonly associated with miscarriage rather than preterm birth, while the anomalies that reduce the physical space available for the fetus tend to produce the opposite pattern.

A single-center study looking at pregnancies in women with uterine malformations found that only about half resulted in a live birth, the cesarean section rate was about two-thirds, and babies born to this group were more likely to need intensive care.²⁵ The most statistically significant complication was preterm delivery. These numbers paint a stark picture, but they come from a referral-center population where more severe cases are overrepresented; women with milder anomalies who deliver uneventfully at community hospitals do not show up in those statistics.

Surgical Options for Congenital Anomalies

Not every uterine anomaly needs treatment. A bicornuate or didelphys uterus, for example, cannot be surgically unified into a normal shape without creating more problems, so management focuses on monitoring pregnancies closely. The septate uterus is the exception: the septum can be cut away hysteroscopically, through the cervix, without any abdominal incision.

A systematic review and meta-analysis of septum resection found that the procedure roughly halved the odds of miscarriage compared to expectant management. The benefit was especially pronounced for women with a complete septum. The same analysis also found a significant reduction in fetal malpresentation and, for partial septa, a decrease in preterm birth.²⁶ A multi-center study of hysteroscopic metroplasty for complete uterine septa further confirmed the procedure’s feasibility and safety, even when cervical or vaginal anomalies complicated the anatomy.²⁷

For bicorporeal (bicornuate) anomalies, abdominal metroplasty is sometimes performed, but the evidence base is much thinner. One retrospective study reported a dramatic jump in take-home baby rate after surgery, but also found that abdominal metroplasty was less effective for septate anomalies than it was for bicorporeal ones, and that the most successful fertility-restoring procedure across all types was actually a cervical cerclage rather than a reconstructive operation.²⁸ The evidence here is mixed enough that treatment decisions tend to be highly individualized, based on a woman’s specific anatomy, reproductive history, and goals.

When a Rudimentary Horn Becomes a Surgical Emergency

A unicornuate uterus with a non-communicating rudimentary horn is one scenario where surgery may be needed outside the context of fertility. Because the horn has no outlet, endometrial tissue trapped inside bleeds with every cycle and the blood has nowhere to go. The result is worsening cyclical pain that builds over months or years, and the standard treatment is laparoscopic removal of the rudimentary horn.⁷ In rare cases, a pregnancy can implant in the rudimentary horn itself. Because the horn’s muscular wall is thin and poorly developed, a growing pregnancy can rupture through it, causing life-threatening internal bleeding. This is a genuine surgical emergency, though fortunately an uncommon one.

The situation is somewhat analogous to an ectopic pregnancy in a fallopian tube, in that the pregnancy is growing in a structure that cannot safely accommodate it. Surgeons can typically remove the horn while preserving the ovary and fallopian tube on that side, which is important for women who still want to conceive using the functioning side of their uterus.

Living With an Undiagnosed Anomaly

Many congenital uterine anomalies go undetected for decades. A woman with a partial septum or a mild bicornuate shape might have somewhat heavier or more painful periods than average but never receive an explanation because standard two-dimensional ultrasound does not always pick these up. The anomaly may only come to light after recurrent miscarriages prompt more detailed imaging, or incidentally during a cesarean section when the surgeon notices something unexpected about the uterine shape.

This delay matters for a couple of reasons. Emotionally, going through repeated pregnancy losses without knowing why is deeply distressing. From a medical standpoint, identifying a septate uterus earlier could lead to a straightforward surgical correction that prevents the next miscarriage. For anomalies that cannot be corrected, knowing about them allows obstetricians to plan for higher-risk pregnancies with closer monitoring, earlier steroid administration if preterm delivery looks likely, and delivery at a facility equipped to handle neonatal complications.

Among acquired abnormalities, the delay pattern is different but still common. Adenomyosis is notoriously difficult to diagnose without MRI, and many women are told their painful, heavy periods are “normal” for years before imaging reveals the characteristic thickening and heterogeneity of the uterine wall. Asherman syndrome can be missed entirely if a woman is not trying to conceive, because lighter periods or absent periods after a uterine procedure may be attributed to hormonal changes rather than scarring. The common thread is that uterine abnormalities, whether congenital or acquired, tend to hide behind symptoms that are easy to dismiss or attribute to something else.