A decidual cast is when your uterine lining sheds in one large piece as compared to drips and drops like your menstrual period. It can be painful, but it’s rare. The large piece of tissue resembles the shape of your uterus. It doesn’t usually cause long-term complications.
A decidual cast is when the lining of your uterus (endometrium) sheds in one piece. Typically, this lining comes out of your vagina gradually during your menstrual period. With a decidual cast, the entire lining of your uterus sheds in one piece at one time. It even takes on the shape of your uterus (an upside down pear or an upside down triangle).
To better understand a decidual cast, it’s helpful to know what’s going on inside your uterus during your menstrual cycle. Over the course of your cycle, your endometrium (lining of your uterus) thickens up. This happens because your body is preparing your uterus for a potential pregnancy. If you don’t get pregnant that cycle, you get your period. This now thick lining sheds over several days, a little bit at a time. With a decidual cast, this thick lining is expelled from your uterus in one large piece of tissue instead of gradually.
Its name comes from the scientific name for thickened endometrial tissue, called a decidual lining. The “cast” is because it sheds in almost the same shape (or cast) of your uterine cavity.
The medical term for a decidual cast is membranous dysmenorrhea.
No, a decidual cast isn’t usually a sign of a serious problem or a medical emergency. However, you should let your healthcare provider know, especially if you’re bleeding heavily or pregnant. Passing tissue from your vagina could be a sign of ectopic pregnancy. If you aren’t pregnant and don’t have any significant symptoms, it’s typically OK to pass a cast.
Decidual casts are rare and the exact number is unknown. It’s most common in pregnant people who experience ectopic pregnancy. An ectopic pregnancy is when a pregnancy occurs outside of your uterus. Decidual casts can happen in people who aren’t pregnant, usually due to progesterone contraceptives.
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A decidual cast can be extremely painful because you’re passing a large piece of tissue through your cervix and out of your vagina. Other symptoms could include:
Symptoms go away once the tissue comes out of your vagina.
A decidual cast is usually red or pink. It’s made up of tissue, mucus and blood and looks “fleshy” like a piece of raw red meat. It may look similar to a clot you’d see during your period, except it’s much larger and has a slightly different texture. It’s shaped like your uterine cavity, which resembles a light bulb.
Of the confirmed cases, most people report decidual casts being about as big as their palm. The exact size varies, but you can expect it to be about as big as a walnut or a small lime.
A decidual cast usually comes out as one big piece of tissue in the shape of your uterus. However, it’s possible it comes out in a few pieces.
Healthcare providers aren’t entirely sure what causes it. Some research shows it may be related to using hormonal contraceptives containing progesterone or ectopic pregnancy. Your healthcare provider will evaluate your symptoms and medical history to see if it could explain passing a decidual cast.
Using hormonal-based contraception may be a factor in passing a decidual cast. This includes birth control pills, implants or injections. There haven’t been enough studies showing a decidual cast is a side effect of taking hormonal birth control. A decidual cast also isn’t a reason not to use hormonal birth control. People undergoing fertility treatment and taking HCG (human gonadotropin) injections have also reported decidual casts.
An ectopic pregnancy is when an embryo implants outside of your uterus, most commonly in your fallopian tube. This is a medical emergency and the pregnancy can’t continue. Your provider will rule out a ruptured ectopic pregnancy as a cause or factor in passing a decidual cast.
Healthcare providers aren’t entirely sure what causes a decidual cast, but they think it might be related to:
There are typically no long-term complications of passing a decidual cast.
No, a decidual cast isn’t a miscarriage. However, they share similar symptoms, like:
Contact your healthcare provider right away if you have any of these symptoms and are pregnant.
Your healthcare provider can determine if the tissue was a decidual cast. To make a diagnosis, your provider may:
If you pass a decidual cast at home, take a picture of it to show your provider or bring it with you to your appointment. Sometimes, your provider can make a diagnosis based on your symptoms and seeing a picture of the tissue.
Since you won’t know for sure if you had a decidual cast until after it passes, there isn’t much you can do to treat it in the moment. If you believe you’re passing a decidual cast, you should take the following precautions:
No, there’s nothing you can do to prevent this rare occurrence. Since it may be related to using hormonal birth control, it may be helpful to talk to your healthcare provider about the risks of hormonal contraceptives. However, the chance of passing a decidual cast isn’t a reason to stop using birth control.
No. Having a decidual cast hasn’t been known to cause infertility.
Passing a decidual cast is rare, and it typically happens to a person just once. While painful, passing a decidual cast doesn’t usually lead to long-term complications. If you think you passed a decidual cast, you should discuss your symptoms with your healthcare provider. They may want to rule out any serious conditions and determine if there’s a cause.
Contact your healthcare provider if you experience any of the following symptoms:
These are common symptoms of many gynecological conditions. It’s best to be cautious and discuss them with a healthcare provider.
A note from Cleveland Clinic
Passing a decidual cast may be a shocking experience. While rare, it can take you by surprise if it happens to you. Rest assured that it’s usually not a sign of anything serious. However, you should still contact your healthcare provider to make sure it’s not something worrisome. It’s especially important to contact your provider if you’re pregnant, as it could be a sign of a problem.
Last reviewed by a Cleveland Clinic medical professional on 02/16/2023.
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