Decidual cast is the term for when the uterus lining leaves the body all at once. A person may experience symptoms such as intense pain and cramping. However, there are no long-term effects associated with the condition.

During a typical menstrual cycle, the uterus lining sheds and leaves the body through the vagina over several days. While rare, a person may experience passing this lining all at once.

This article further explains a decidual cast, including the symptoms and causes. It also discusses complications, risk factors, and prevention of a decidual cast.

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This feature mentions pregnancy loss, stillbirth, or both. Please read at your own discretion.

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In a typical menstrual cycle, the uterus creates a lining called the endometrium. The biological purpose of the endometrium is to:

  • act as an area for a fertilized egg to implant
  • help maintain a pregnancy if it occurs
  • shed as part of the menstrual cycle if pregnancy does not occur

The endometrium typically detaches and sheds gradually over several days. However, for some people, this shedding happens all at once. If this occurs, the endometrium may come out as one complete piece, called a decidual cast.

The medical name for a decidual cast is membranous dysmenorrhea. Exact data on the prevalence of decidual casts does not exist, but experts believe it is rare.

Appearance

The name contains the word “cast” because the tissue that exits the body maintains the roughly triangular shape and size of the person’s uterus. For reference, a typical uterus measures 8 centimeters (cm) long, 5 cm wide, and 4 cm thick.

Decidual cast tissue generally feels fleshy, similar to a piece of skin. It can appear shiny and may be:

  • gray
  • pink
  • white
  • red
  • black
  • cream

In some instances, the cast may be very dark and resemble a large blood clot. Blood may also come out with it. The cast may feel solid or as though it contains fluid.

Symptoms that accompany a decidual cast may include:

These symptoms typically resolve quickly after the decidual cast leaves the body.

Passing a decidual cast can be alarming, especially if a person does not know what it is or has not experienced it before. However, a 2015 case report suggests a low recurrence rate and no known long-term effects are associated with the condition.

There is no single cause for all decidual casts. Some people may never experience one, while others may experience multiple occurrences. However, this is rare.

Ectopic pregnancy

The Ectopic Pregnancy Trust explains that an ectopic pregnancy can lead to a decidual cast forming. This is because hormones do not function as they should during an ectopic pregnancy, which can result in a sharp drop in hormone levels. This drop can cause the uterus to suddenly shed its tissue.

Bleeding can also follow an ectopic pregnancy, and doctors often prescribe methotrexate to treat it. Methotrexate is a type of medication called immunosuppressant. These types of drugs help slow down the immune system and decrease inflammation.

In some cases, bleeding treated with methotrexate can be heavy and may include blood clots. A decidual cast may occur as part of this.

As ectopic pregnancy can be life threatening, it is important for doctors to rule out this possibility if a person passes a decidual cast.

Hormonal birth control

A 2021 review on decidual casts found that 43% of pediatric cases had associations with depo-medroxyprogesterone acetate (DMPA). This is a contraceptive injection widely known as the Depo-Provera shot.

The review noted another 43% of occurrences were associated with combined oral birth control, known informally as “the pill.” Finally, 14% of cases occurred in people using the ethinyl estradiol/norelgestromin birth control patch.

A 2022 survey found that 11% of people who reported experiencing a decidual cast were taking hormonal birth control.

Hormonal changes

During the menstrual cycle, the progesterone level in the body rises. This is the body’s way of preparing the uterus for the implantation of a fertilized egg.

If implantation does not occur, the progesterone level falls. This typically causes the endometrium to break up and disintegrate. However, this step may not always occur after progesterone decreases, leading to the formation of a decidual cast.

COVID-19 vaccination

A 2022 study theorized that COVID-19 vaccination may have links with increased reports of decidual cast occurrence. Researchers speculated that the vaccine could lead to menstrual irregularities, which in turn may lead to decidual casts.

The researchers acknowledged that this is theoretical and the irregularities could result from multiple other mechanisms. It is also important to note that vaccines are safe, rigorously tested ways to protect against diseases such as COVID-19.

Learn more about how vaccines work and vaccines for COVID-19.

Decidual casts are rare, and many other conditions can produce similar symptoms. Therefore, it is important for a doctor to rule out other conditions before diagnosing a decidual cast.

A doctor will typically begin by asking questions about a person’s symptoms, including duration and severity. They may also ask about family history, whether a person has experienced anything similar before, and whether they have any preexisting conditions relating to menstruation or the reproductive organs.

A doctor may also ask for a description of the cast, including its color, shape, and size. It may help for a person to take photographs of the cast. Or, if they are comfortable doing so, they may wish to bring the mass in a clean, tightly sealed container.

The typical next step is a physical examination. A doctor may ask a person to lie down so they can gently examine their abdomen. They may also perform a pelvic exam, which can include visual checks and specialized tools for thorough inspection.

Similar conditions

Examples of conditions that can appear similar to a decidual cast include:

  • Menstrual blood clot: Very heavy periods can often include large blood clots. It is possible for clots to be larger than a quarter in some cases. Symptoms associated with periods can overlap with those of decidual casts.
  • Pregnancy loss: A decidual cast can resemble a gestational sac, so it is important for doctors to rule out this possibility to provide the correct treatment. A doctor may request a person takes a pregnancy test.
  • Foreign body: In some cases, what a person suspects to be a decidual cast turns out to be a foreign body leaving the vagina. A common example is a forgotten tampon.
  • Fibroepithelial cervical polyps (FEPs): These are large, noncancerous growths that develop on the cervix. FEPs can protrude out of the vagina and may cause vaginal bleeding. A person may mistake the protrusion for a decidual cast.
  • Sarcoma botryoides: This is a cancerous tumor that can occur in the vagina. Similar to FEPs, the growth can protrude out of the vagina and cause vaginal bleeding.
  • Rhabdomyosarcoma: This type of cancer can develop in female reproductive organs, such as the cervix. It most commonly presents as a solid protruding mass accompanied by vaginal bleeding.

A 2021 case report explains a known association between the use of, or stopping the use of, various types of hormonal birth control and decidual casts. The report specifically notes the long-term use of injectable DMPA and its link to the formation of a decidual cast in one person.

A 2022 review of three case studies suggests that certain factors may contribute to a person’s risk of experiencing a decidual cast. Factors include:

  • Age: The researchers suggest that people ages 9–41 years may be more likely to experience a decidual cast.
  • Hormonal birth control: All the people involved in the review had recently taken hormonal birth control.
  • Irregular periods: All participants also experienced irregular periods.
  • Race: A 2022 survey found that those who reported a decidual cast were predominantly white.

A 2016 case report described the occurrence of a decidual cast in a 13-year-old taking hormonal birth control to treat atypical uterine bleeding.

A 2015 case report also reported decidual cast occurrence in a 32-year-old taking combined oral birth control for heavy menstrual bleeding. The researchers noted associations between decidual casts and the following medications and medication ingredients:

  • drospirenone
  • cyproterone
  • norgestimate
  • desogestrel
  • norethindrone acetate
  • transdermal patch
  • injectable DMPA

It is important to note that case studies focus on specific individuals, so their findings may not always be widely applicable.

Experts generally consider decidual casts to be harmless and self-resolving. This means that symptoms typically go away soon after the cast leaves the body. There is also a low rate of recurrence.

However, a decidual cast can cause complications in extremely rare cases. A 2021 case study reported on the occurrence of an infected decidual cast that also contained products of conception or remnants from a pregnancy loss.

The researchers theorized that the person had stopped receiving DMPA, had become pregnant, and a decidual cast had formed around the products of conception. The decidual cast and products of conception then came away from the uterus but did not leave the body, which led to infection.

If a person experiences symptoms associated with a decidual cast, they may wish to contact a doctor to discuss them.

However, if a person also experiences severe symptoms, such as intense pain, cramping, or heavy bleeding, they should seek emergency medical help. Some conditions can cause symptoms similar to decidual casts, which may require immediate intervention.

A doctor may recommend a pregnancy test to rule out conditions such as ectopic pregnancy or pregnancy loss. If a pregnant person experiences vaginal bleeding or abdominal pain or passes tissue from their vagina, they should contact a doctor immediately.

A decidual cast is likely not preventable. It can occur due to a variety of factors outside a person’s control, such as irregular periods.

As the causes of decidual casts are still largely unknown, there is no full understanding of what a person may be able to do to avoid them.

Case reports suggest a link between hormonal birth control and decidual casts, but experts cannot conclusively confirm this without wider research.

Below are answers to some common questions about decidual casts.

How does a decidual cast differ from pregnancy loss?

A decidual cast can occur regardless of whether someone is pregnant. A person must be pregnant for pregnancy loss to occur.

However, symptoms associated with both conditions can overlap. Both may include a person passing tissue from the vagina. They may also come with intense pain and vaginal bleeding.

An individual who could be pregnant and experiences symptoms of a decidual cast should seek emergency medical assistance. Decidual casts can mimic other, more serious conditions that require immediate care. For example, an ectopic pregnancy can be life threatening.

Is passing a decidual cast routine?

Decidual casts are rare, meaning a person is unlikely to experience one. However, when they do occur, decidual casts are not typically a cause for concern.

An individual may wish to contact a doctor if they have questions or concerns about passing a decidual cast.

Decidual casts are rare and can cause severe pain. However, symptoms typically resolve as the cast leaves the body. They are not typically an indicator of a serious condition.

Passing a decidual cast can be an alarming experience, so a person may wish to contact a doctor if they have concerns. A pregnant person or individuals experiencing severe or ongoing symptoms should seek emergency medical assistance.