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Uterine shape is determined prior to birth in the developing embryo and therefore, women are born with uterine anomalies. By definition, these problems are "congenital": a medical problem present since birth.

Types of Uterine Abnormalities

Hypoplasia/Agenesis

uterine hypoplasia (uterus which is small in its totality), narrowing of the cavity, strictions, uterine diverticula.

A women may lack a vagina, a cervix (the bottom one-third of the uterus which opens into the vagina), the fallopian tubes or the entire vagina and body of the uterus (except for the fundus). This occurs from a developmental problem with a section of both of the mullerian ducts. These anomalies are commonly associated with urinary tract anomalies because the structures which give rise to the urinary tract lie close to the mullerian ducts and are affected by the same injurious insult.

Some gynecologists are recommending hysteroscopic metroplasty--a surgical procedure to enlarge the uterus--

Unicornuate

uterus unicornis - with a second blind-ending rudimentary horn

When one of the mullerian ducts fails to form, a single horn (banana-shaped) uterus develops from the healthy mullerian duct. This single horn uterus may stand alone. However, in 65% of women with a unicornuate uterus, the remaining mullerian duct may form an incomplete (rudimentary) horn. There may no cavity in this rudimentary horn or it may have a small space within it, but no opening which communicates with the unicornuate uterus and vagina. In the latter case, a girl may have monthly pain during adolescence because there is no outlet for the menses from this rudimentary horn. This pain would lead to identification of this problem. In some cases, the rudimentary horn contains a cavity that is continuous with the healthy single horn uterus, but much smaller than the cavity within the healthy uterus. There is a risk that a pregnancy will implant in this rudimentary horn, but because of space limitations, 90% of such pregnancies rupture.

Didelphus

uterus didelphys- entirely double uterus ie. two single-horned uteruses

A doubled uterus results from the complete failure of the two mullerian ducts to fuse together (stage 1 of development). So each duct develops into a separate uterus each of which is narrower than a normal uterus and has only a single horn. These two uteri may each have a cervix or they may share a cervix. In 67% of cases, a didelphus uterus is associated with two vagina separated by a thin wall.

Bicornuate

uterus bicornis unicollis -two single-horned uteruses

Defects in the development of the uterus can also lead to reproductive problems. An abnormally shaped uterus or cervix may result in complications once pregnancy has been achieved including miscarriage and premature labor. Many women have carried successful pregnancies to term, most will deliver via C-Section, but some can also deliver vaginally. The breech position is also common with this type of abnormality because the baby has less room to turn into the head down position during the 3rd trimester.

This is the most common congenital uterine anomaly. It results from a failure of fusion between the mullerian ducts at the 'top'. This failure may be "complete" which results in a two separate single horn uterine bodies sharing one cervix. Alternatively, in a "partial" bicornuate uterus fusion between the mullerian ducts occurred at the 'bottom', but not the 'top'. Thus, there is a single uterine cavity at the bottom with a single cervix, but it branches into two distinct horns at the top. Since the ducts never fused at the top, these two horns are separate structures when seen from the outside of the uterus.

Septate

uterus subseptae - uterus has midline septum

A septate uterus results from a problem in stage 2 or 3 of uterine development. The two mullerian ducts fused normally; however, there was a failure in degeneration of the median septum. If this failure was "complete", a median septum persists in the entire uterus separating the uterine cavity into two single-horned uteri which share one cervix. If this failure was "partial", resorption of the lower part of the median septum occured in stage 2, but the top of the septurn failed to dissolve in stage 3. Hence, there is a single cervix and uterine cavity at the bottom, but at the top that cavity divides into 2 distinct horns. Since this uterine anomaly occurs later in uterine development after complete duct fusion, the external shape of the uterus is a single unit (normal appearing). This is distinct from the bicornuate uterus which can be seen branching into two distinct horns when viewed from the outside.

Arcuate

uterus arcuatus - uterus slightly indented in the middle

This type of uterus is essentially normal in shape with a small, midline indentation in the uterine fundus which results from failure to completely dissolve the median septurn. This is given a distinct classification because it does not seem to have any negative effects on pregnancy.

DES- Drug Exposure

diethylstilbestrol (DES) exposure – Exposure to DES during fetal life

May result in the development of a small or a T-shaped uterus. There is an increased risk of pregnancy in the Fallopian tubes (ectopic pregnancy), as well as problems with carrying the pregnancy to term due to the small size of the uterus. In general, the smaller the uterus, the more likely the chances for complications. Additionally, the lining may be deficient in these patients lowering the likelihood of pregnancy altogether.

Any woman born before 1977 should be systematically screened for DES exposure in the following clinical situations:

fertility testing
ectopic pregnancy
repeated first trimester and, particularly, second trimester miscarriages
premature delivery

Any pregnancy in a young woman who was exposed to DES in utero should automatically be considered a risk pregnancy. In the vast majority of cases, however, the outcome of these pregnancies is completely normal.

Women should be given information on the increased risk of ectopic pregnancy, early and late miscarriage, and premature delivery, often with no warning contractions.

It is therefore important to verify that the ovum is located inside the uterus and to perform twice monthly checks of the cervix.

The need for early prevention measures, such as rest, reduced activity, work leave, home monitoring by a midwife, or even hospitalization, should be assessed on the basis of the individual's obstetrical history, and any uterine or cervical abnormality which regular monitoring may uncover.

Generally speaking, rest during the early phase of pregnancy is recommended as the risk of prematurity is of the same order of magnitude as in the case of a twin pregnancy. Rest is an essential element in the prevention of miscarriage and prematurity. Cerclage of the cervix is indicated in some cases.

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How would a doctor detect a uterine anomaly?

Frequently, uterine anomalies go undetected until a woman has a baby. At that time, if the doctor needs to explore the uterine cavity after delivery, he or she may discover that it has an unusual shape. Alternatively, if a cesarean section is performed, the unusual shape of the uterus may be noted at that time.

Uterine anomalies can be associated with recurrent pregnancy loss, preterm delivery, intrauterine fetal growth restriction and an abnormal fetal presentation (any part other than the top (vertex) of the fetal head facing the cervix). Evaluation of these symptoms may include evaluation for a uterine anomaly. A uterine anomaly can be diagnosed by a combination of several techniques: ultrasound, magnetic resonance imaging (MRI), hysterosalpinography, hysteroscopy, or laparascopy.

Both ultrasound and MRI involve external imaging of the uterus. Ultrasound is somewhat less sensitive than other techniques - it may miss some anomalies, but it is relatively inexpensive, a short procedure and particularly good for determining whether there is a cavity in the rudimentary horn of a unicornuate uterus. If an intrauterine septum is seen with ultrasound, an MRI might be recommended. MRI is more expensive, more time consuming and less readily available, but it will give a good picture of the external border of the uterus which is important to distinguish a bicornuate from a septate uterus.

Hysteroscopy is a procedure in which the cervix is dilated and a camera is inserted within the uterus to visualize the inside. This technique allows not only diagnosis, but also in some cases repair of an intrauterine septurn (e.g. in a septate uterus) can be performed through the cervix with the assistance of this visualization. Hysterosalpinography involves the introduction of a dye into the uterus through a thin tube followed by X-ray of the uterus. In an X-ray, this dye shows the outline of the intrauterine cavity. The drawback of this technique is that the intrauterine cavity may have the same shape in a bicornuate or septate uterus. So MRI or laparoscopy are needed to "visualize" the outside of the border to allow distinction between bicornuate and septate uterus. Laparoscopy involves insertion of a camera through a small incision in the abdomen under anesthesia. This is technique is used usually only in a more complicated diagnosis and it can also be used to assist the repair of an intrauterine septurn by hysteroscopy.

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References:

The American Fertility Society. "The AFS classifications of adnexal adhesions, distal tube occlusion, tubal occlusion secondary to tubal ligation, tubal pregnancies, Mullerian anomalies and interuterine adhesions." In Fertility and Sterility 1988; 49:944.