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Decidual Cast: What It Is, What Causes It, and How It's Treated

This shedding of the uterine lining in one piece during your period is rare, but can be painful. Here’s what you need to know


During a menstrual cycle, the uterus goes through various changes to prepare for pregnancy. First of all, the endometrium (lining of the uterus) grows thick and spongy to help a fertilized egg grow into an embryo, then a fetus. Progesterone is the key hormone here. If an egg isn’t fertilized (meaning you’re not pregnant), progesterone levels drop and the endometrium breaks down, coming out of your vagina along with menstrual blood (as you’re having your period). Most of the time, the endometrial lining bleeds gradually in a thin, watery fashion. But sometimes the whole endometrium is sloughed off and comes out in one large piece, known as a decidual cast. Here’s everything you need to know about this rare occurrence, from possible causes to how to manage it.



What Does a Decidual Cast Look Like?

A decidual cast often takes the shape of the uterus, which can look like a cone or a triangle. This is why it’s called a cast (just like a cast of your arm if you need one for a broken bone). Since an adult uterus is about three inches long and two inches wide, that’s the size a decidual cast would be, too. According to a case report published, a decidual cast may look like a fleshy mass or blob, made up of whitish-gray or grayish-brown tissue and blood.


Symptoms of Decidual Cast

Signs of a decidual cast are similar to that of a period. These include:


  • Cramps

  • Dizziness

  • Lightheadedness

  • Nausea

  • Pelvic pain

  • Vaginal bleeding


However, a decidual cast is likely to feel much more intense than a regular period. Because the cast comes out all at once, like a big blood clot, the cramps can be much more uncomfortable than usual period cramps.


Causes of Decidual Cast

Decidual casts are rare, and experts don’t know a precise number of cases. Plus, the lack of medical knowledge and underdiagnosis means doctors haven’t been able to pinpoint an exact cause. Some people get a decidual cast once, from nowhere and without risk factors, and then never again. Other people have several of them throughout their lifetime. Decidual casts are more common in situations where hormones are building, such as with ectopic pregnancy or hormone contraceptives. Some researchers suggest that a surge of both estrogen and progesterone in these situations may cause the spontaneous expulsion of the uterine lining.


Hormonal Contraceptives

According to one report, most people known to have had a decidual cast were on hormonal birth control or hormonal therapies of some kind (including those taken orally, by injection, or implant). Another study noted that most recorded cases involved people who had taken contraceptives containing progesterone. A decidual cast can happen with oral contraceptive pills or Depo-Provera (the contraceptive injection). This can cause a tremendous amount of cramping which is termed ‘membranous dysmenorrhea.’


Ectopic Pregnancy

Per an article published, a decidual cast may be linked to an ectopic pregnancy, which is a pregnancy that occurs when an egg is fertilized outside the uterus, commonly in a fallopian tube. However, the exact relationship remains unclear. Because passing tissue from your vagina could be a sign of ectopic pregnancy, your doctor will look to rule this out as a factor (via a pregnancy test and potentially an ultrasound) in the occurrence of a decidual cast.


Can a Decidual Cast Be Diagnosed?

A decidual cast isn’t a condition that can be diagnosed before the endometrium passes out of the vagina. You will only know if you had a decidual cast after it passes. There is also no definitive way to prevent or treat them. To manage the symptoms, it is suggested using heating pads and ibuprofen or acetaminophen. Try taking the tissue (or a picture of it) to your healthcare provider to help them confirm whether it’s a decidual cast. To do this, they may perform a pelvic exam and a physical exam and order imaging tests (such as a pelvic ultrasound) to check the uterus. They’ll also take details of your symptoms and any medications you’re taking, including birth control, and do a pregnancy test.


When to See a Healthcare Provider

Studies have shown that women have no long-term health impacts after passing a decidual cast, but it is strongly advised contacting your physician if it happens to you.


Additionally, you should contact your doctor right away if you experience either:

  • Painful menstrual cramps and vaginal bleeding that’s not what you usually experience during your monthly period

  • A prolonged or heavy period that’s causing more discomfort than usual


It’s possible that these could be symptoms of a decidual cast or another gynecological condition (including uterine cancer). A decidual cast is not a miscarriage, but the symptoms can be similar: cramping, pain, vaginal bleeding, and the loss of large pieces of tissue. Speak to your doctor if you think you might be pregnant and have these symptoms. And if you suspect an ectopic pregnancy, contact 911 or your local emergency services. This is a potentially life-threatening condition. Although a decidual cast is rare and unlikely to be a sign of anything serious, it may be a shock to pass such a large piece of tissue. Getting checked out by your doctor will help to put your mind at ease.


Adapted from: Health Central



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