A bicornuate uterus or bicornate uterus (from the Latin "cornū", meaning "horn"), commonly referred to as a "heart-shaped" uterus, is a uterus composed of two "horns" separated by a septum. In humans, a bicornuate uterus is a type of uterine malformation, but in some other mammalian species, including rodents and pigs, it is normal.

It is possible to diagnose a bicornuate uterus using gynecologic ultrasonography, specifically sonohysterography, and MRI. However, as there is no indication to do such procedures on asymptomatic women, the presence of a bicornuate uterus may not be detected until pregnancy or delivery.

In a C-section (usually done due to malpresentation), the irregular shape of the uterus will be apparent.

Other less reliable diagnostic imaging methods include hysterosalpingography and hysteroscopy; these procedures are typically done during the course of an infertility investigation.

A unicornuate uterus represents a uterine malformation where the uterus is formed from one only of the paired Müllerian ducts while the other Müllerian duct does not develop or only in a rudimentary fashion. The sometimes called "hemi-uterus" has a single horn linked to the ipsilateral fallopian tube that faces its ovary.

The American Fertility Society (now American Society of Reproductive Medicine) Classification distinguishes:

- Class I: Müllerian agenesis (absent uterus).

- Uterus is not present, vagina only rudimentary or absent. The condition is also called Mayer-Rokitansky-Kuster-Hauser syndrome. The patient with MRKH syndrome will have primary amenorrhea.

- Class II: Unicornuate uterus (a one-sided uterus).

- Only one side of the Müllerian duct forms. The uterus has a typical "banana shape" on imaging systems.

- Class III: Uterus didelphys, also uterus didelphis (double uterus).

- Both Müllerian ducts develop but fail to fuse, thus the patient has a "double uterus". This may be a condition with a double cervix and a vaginal partition (v.i.), or the lower Müllerian system fused into its unpaired condition. See Triplet-birth with Uterus didelphys for a case of a woman having spontaneous birth in both wombs with twins.

- Class IV: Bicornuate uterus (uterus with two horns).

- Only the upper part of that part of the Müllerian system that forms the uterus fails to fuse, thus the caudal part of the uterus is normal, the cranial part is bifurcated. The uterus is "heart-shaped".

- Class V: Septated uterus (uterine septum or partition).

- The two Müllerian ducts have fused, but the partition between them is still present, splitting the system into two parts. With a complete septum the vagina, cervix and the uterus can be partitioned. Usually the septum affects only the cranial part of the uterus. A uterine septum is the most common uterine malformation and a cause for miscarriages. It is diagnosed by medical image techniques, i.e. ultrasound or an MRI. MRI is considered the preferred modality due to its multiplanar capabilities as well as its ability to evaluate the uterine contour, junctional zone, and other pelvic anatomy. A hysterosalpingogram is not considered as useful due to the inability of the technique to evaluate the exterior contour of the uterus and distinguish between a bicornuate and septate uterus.

A uterine septum can be corrected by hysteroscopic surgery.

- Class VI: DES uterus.

- The uterine cavity has a "T-shape" as a result of fetal exposure to diethylstilbestrol.

An additional variation is the arcuate uterus where there is a concave dimple in the uterine fundus within the cavity.

A rudimentary uterus is a uterine remnant not connected to cervix and vagina and may be found on the other side of an unicornuate uterus.

Patients with uterine abnormalities may have associated renal abnormalities including unilateral renal agenesis.

Uterus didelphys (sometimes also "uterus didelphis") represents a uterine malformation where the uterus is present as a paired organ when the embryogenetic fusion of the Müllerian ducts fails to occur. As a result, there is a double uterus with two separate cervices, and rarely a double vagina as well. Each uterus has a single horn linked to the ipsilateral fallopian tube that faces its ovary.

In non human species ("e.g." nematodes), a didelphic genital tract may be normal rather than a malformation. Such species are described as didelphic, as opposed to monodelphic, with a single tract.

The arcuate uterus is a form of a uterine anomaly or variation where the uterine cavity displays a concave contour towards the fundus. Normally the uterine cavity is straight or convex towards the fundus on anterior-posterior imaging, but in the arcuate uterus the myometrium of the fundus dips into the cavity and may form a small septation. The distinction between an arcuate uterus and a septate uterus is not standardized.

A specific association of uterus didelphys (double uterus), unilateral hematocolpos (inadequate draining of menstrual blood) and ipsilateral renal agenesis (having only one kidney) has been described.

Women with the condition may be asymptomatic and unaware of having a uniconuate uterus; normal pregnancy may occur. In a review of the literature Reichman et al. analyzed the data on pregnancy outcome of 290 women with a unicornuate uterus. 175 women had conceived for a total of 468 pregnancies. They found that about 50% of patients delivered a live baby. The rates for ectopic pregnancy was 2.7%, for miscarriage 34%, and for preterm delivery 20%, while the intrauterine demise rate was 10%. Thus patients with a unicornuate uterus are at a higher risk for pregnancy loss and obstetrical complications.

A uterine septum is a form of a congenital malformation where the uterine cavity is partitioned by a longitudinal septum; the outside of the uterus has a normal typical shape. The wedge-like partition may involve only the superior part of the cavity resulting in an "incomplete septum" or a "subseptate uterus", or less frequently the total length of the cavity ("complete septum") and the cervix resulting in a double cervix. The septation may also continue caudally into the vagina resulting in a "double vagina".

The following table distinguishes among some of the terms used for the position of the uterus:

A retroverted uterus should be distinguished from the following:

Additional terms include:

- "retrocessed uterus:" both the superior and inferior ends of the uterus are pushed posteriorly

- "severely anteflexed uterus:" the uterus is in the same position as "normal" and bends in the same direction (concave is anterior) but the bend is much more pronounced

- "vertical uterus:" the fundus (top of the uterus) is straight up.

As the vagina is largely derived from the Müllerian ducts, lack of fusion of the two ducts can lead to the formation of a vaginal duplication and lack of absorption of the wall between the two ducts will leave a residual septum, leading to a "double vagina". This condition may be associated with a uterus didelphys or a uterine septum. Since the condition is internal and usually asymptomatic, a person may not be aware of having a "double vagina." If necessary, the partition can be surgically corrected, however, there is no valid medical reason for such a procedure.

In most cases, a retroverted uterus is genetic and is perfectly normal but there are other factors that can cause the uterus to be retroverted. Some cases are caused by pelvic surgery, pelvic adhesions, endometriosis, fibroids, pelvic inflammatory disease, or the labor of childbirth.

It is often characterized by a decrease in flow and duration of bleeding (absence of menstrual bleeding, little menstrual bleeding, or infrequent menstrual bleeding) and become infertile. Menstrual anomalies are often but not always correlated with severity: adhesions restricted to only the cervix or lower uterus may block menstruation. Pain during menstruation and ovulation is sometimes experienced and can be attributed to blockages.

It has been reported that 88% of AS cases occur after a D&C is performed on a recently pregnant uterus, following a missed or incomplete miscarriage, birth, or during an elective termination (abortion) to remove retained products of conception.

Molar pregnancies usually present with painless vaginal bleeding in the fourth to fifth month of pregnancy. The uterus may be larger than expected, or the ovaries may be enlarged. There may also be more vomiting than would be expected (hyperemesis). Sometimes there is an increase in blood pressure along with protein in the urine. Blood tests will show very high levels of human chorionic gonadotropin (hCG).

A pelvic examination may reveal a double vagina or double cervix that should be further investigated and may lead to the discovery of a uterine septum. In most patients, however, the pelvic examination is normal. Investigations are usually prompted on the basis of reproductive problems.

Helpful techniques to investigate a septum are transvaginal ultrasonography and sonohysterography, MRI, and hysteroscopy. More recently 3-D ultrasonography has been advocated as an excellent non-invasive method to delineate the condition. Prior to modern imaging hysterosalpingography was used to help diagnose the uterine septum, however, a bicornuate uterus may deliver a similar image.

An important category of septate uterus is the hybrid type a variant that may be misdiagnosed as bicornuate uterus when seen by laparoscopy Professor El Saman From Egypt was the first to describe this anomaly and warned gynecologist about this common misdiagnosis, whenever there is a uterine fundus depression on laparoscopy gynecologists should compare the depth of this depression with the depth of the dividing internal interface. Hybrid septate uterus benefit from hysteroscopic metroplasty under laparoscopic control.

Various classification systems were developed to describe Asherman’s syndrome (citations to be added), some taking into account the amount of functioning residual endometrium, menstrual pattern, obstetric history and other factors which are thought to play a role in determining the prognoses. With the advent of techniques which allow visualization of the uterus, classification systems were developed to take into account the location and severity of adhesions inside the uterus. This is useful as mild cases with adhesions restricted to the cervix may present with amenorrhea and infertility, showing that symptoms alone do not necessarily reflect severity. Other patients may have no adhesions but amenorrhea and infertility due to a sclerotic atrophic endometrium. The latter form has the worst prognosis.

Symptoms and signs in the newborn can be sepsis, abdominal mass, and respiratory distress. Other abdominopelvic or perineal congenital anomalies frequently prompt radiographic evaluation in the newborn, resulting in a diagnosis of coincident vaginal atresia. Symptoms for vaginal atresia include cyclical abdominal pain, the inability to start having menstrual cycles, a small pouch or dimple where a vaginal opening should be, and pelvic mass when the upper vagina becomes filled with menstrual blood. Signs and symptoms of vaginal atresia or vaginal agenesis can often go unnoticed in females until they reach the age of menstruation. Women may also experience some form of abdominal pain or cramping.

A vaginal septum is a congenital partition within the vagina; such a septum could be either longitudinal or transverse.

Patients with cervical agenesis typically present in early adolescence, around the time of menarche, with amenorrhea and cyclic pelvic pain caused by the obstruction of menstrual flow from the uterus.

A boggy uterus is a finding upon physical examination where the uterus is more flaccid than would be expected.

It can be associated with uterine atony.

It may also be associated with adenomyosis.

Up to 10% of women with ectopic pregnancy have no symptoms, and one-third have no medical signs. In many cases the symptoms have low specificity, and can be similar to those of other genitourinary and gastrointestinal disorders, such as appendicitis, salpingitis, rupture of a corpus luteum cyst, miscarriage, ovarian torsion or urinary tract infection. Clinical presentation of ectopic pregnancy occurs at a mean of 7.2 weeks after the last normal menstrual period, with a range of 4 to 8 weeks. Later presentations are more common in communities deprived of modern diagnostic ability.

Signs and symptoms of ectopic pregnancy include increased hCG, vaginal bleeding (in varying amounts), sudden lower abdominal pain, pelvic pain, a tender cervix, an adnexal mass, or adnexal tenderness. In the absence of ultrasound or hCG assessment, heavy vaginal bleeding may lead to a misdiagnosis of miscarriage. Nausea, vomiting and diarrhea are more rare symptoms of ectopic pregnancy.

Rupture of an ectopic pregnancy can lead to symptoms such as abdominal distension, tenderness, peritonism and hypovolemic shock. A woman with ectopic pregnancy may be excessively mobile with upright posturing, in order to decrease intrapelvic blood flow, which can lead to swelling of the abdominal cavity and cause additional pain.

Molar pregnancy is an abnormal form of pregnancy in which a non-viable fertilized egg implants in the uterus and will fail to come to term.

A molar pregnancy is a gestational trophoblastic disease which grows into a mass in the uterus that has swollen chorionic villi. These villi grow in clusters that resemble grapes. A molar pregnancy can develop when a fertilized egg does not contain an original maternal nucleus. The products of conception may or may not contain fetal tissue. It is characterized by the presence of a hydatidiform mole (or hydatid mole, mola hydatidosa). Molar pregnancies are categorized as partial moles or complete moles, with the word "mole" being used to denote simply a clump of growing tissue, or a "growth".

A complete mole is caused by a single sperm (incidence is about 90%) or two (incidence is about 10%) sperms combining with an egg which has lost its DNA (in the first case the sperm then reduplicates forming a "complete" 46 chromosome set). The genotype is typically 46,XX (diploid) due to subsequent mitosis of the fertilizing sperm, but can also be 46,XY (diploid). 46,YY (diploid) is not observed. In contrast, a partial mole occurs when a haploid egg is fertilized by two sperm or by one sperm which reduplicates itself yielding the genotypes of 69,XXY (triploid) or 92,XXXY (tetraploid). Complete hydatidiform moles have 2 - 4% risk of developing into choriocarcinoma in Western countries and 10 - 15% in Eastern countries and overall, also a 15% chance of becoming an invasive mole. Incomplete moles can become invasive (<5% risk) but are not associated with choriocarcinoma. Complete hydatidiform moles account for 50% of all cases of choriocarcinoma.

The major differential diagnosis is the uterine septum. The lack of agreement to separate these two entities makes it difficult to assess the results in the literature.

Cervical agenesis is a congenital disorder of the female genital system that manifests itself in the absence of a cervix, the connecting structure between the uterus and vagina. Milder forms of the condition, in which the cervix is present but deformed and nonfunctional, are known as cervical atresia or cervical dysgenesis.

Hematometra typically presents as cyclic, cramping pain in the midline of the pelvis or lower abdomen. Patients may also report urinary frequency and urinary retention. Premenopausal women with hematometra often experience abnormal vaginal bleeding, including dysmenorrhea (pain during menstruation) or amenorrhea (lack of menstruation), while postmenopausal women are more likely to be asymptomatic. Due to the accumulation of blood in the uterus, patients may develop low blood pressure or a vasovagal response. When palpated, the uterus will typically feel firm and enlarged.