For most uterus owners, periods are a monthly occurrence as regular—and annoying!—as rent. And between bleeding, PMS symptoms, and the cost of period products, it's not always a great time. But there's a very rare, even more uncomfortable phenomenon that some women can experience instead of a period—and people have recently been sharing their stories about it on TikTok. That phenomenon? A decidual cast.
This is a female health condition that happens when your body isn't quite working as it's supposed to. A regular period involves your uterus shedding its lining across a series of days. When you have a decidual cast, your uterus evacuates all of its lining in one go, and it emerges in the shape of the womb. It's not thought to be health-threatening, but it can be incredibly disturbing, especially if you don't know what's happening to you.
That's why we talked to some experts to get the low-down on exactly what a decidual cast is, why it happens, when to worry, and what it means for you if you experience one. (As always, if you're experiencing any health scares, talk to your GP. It's always better to err on the side of caution.) Let's get into it.
What is a decidual cast?
First, let's revisit some basic physiology. Each month, the lining of your womb (or endometrium) thickens up. This thickened endometrial tissue is called a "decidual lining."
Normally, if you're not pregnant, you'll experience a monthly bleed. Across the course of five-to-seven days, you shed a combination of that endometrium and period blood in dribs and drabs. Dr. Deborah Lee, a Sexual and Reproductive Health Specialist, explains that this is why your "period blood can look lumpy and irregular."
But, as noted, a decidual cast happens when the entire womb lining is shed at once: "Instead of shedding the decidual lining little by little as you normally do, the entire decidual lining is expelled all in one go," Dr. Lee explains. Unfortunately, this can come with a lot of pain.
What does a decidual cast look like?
A decidual cast is a fleshy mass of intact tissue that is often triangular, in the shape of the uterus. It is typically red, pink, or flesh-colored, and some people compare it to the look and feel of a placenta. A paper in Internet Scientific Publications features three images of a decidual cast, should you like to take a look.
What is it like to experience a decidual cast?
Curious what passing a decidual cast feels like? These two viral videos from TikTok users @majdamedved and @sweglestory shed a little light on the often-unpleasant experience:
Why do women experience a decidual cast?
The good news is that "having a decidual cast is very rare," according to Dr. Lee, who says that in over three decades of working in General Practice and Community Sexual and Reproductive Health clinics, she has only ever seen one patient with a decidual cast.
Dr. Lee notes that a decidual cast is most common in women between the ages of 20 to 40 who have experienced an ectopic pregnancy. This is when a fertilized egg implants itself outside of the womb. The aforementioned paper in Internet Scientific Publications comes to the same conclusion—decidual casts are most common in pregnant women, especially those who have ectopic pregnancies. Though the signs can mimic a miscarriage, a decidual cast is different, so you should always consult your doctor.
But, as per the paper, there have been reported instances of non-pregnant women experiencing a decidual cast, too. This has been attributed to the side effects of hormones used in fertility treatments (like human menopausal gonadotrophin), as well as progestogens, which are hormones mimicking progesterone that are used widely for hormonal contraception. The latter of which may be especially concerning for many people who use hormonal birth control.
Dr. Lee offers some reassurance: "There is absolutely no need to stop using your contraception because of fear over having a decidual cast. It's very important to continue taking your contraception correctly and carefully," she says.
What do I do if I think I've experienced a decidual cast?
First thing: don't panic. Although rare, you are not alone. But, as previously mentioned, Dr. Lee explains that having a decidual cast is "likely to be very unpleasant."
"It's extremely painful, partly because of the physical passage of such a large piece of tissue through your cervix (neck of the womb)," she says. Other symptoms may also include dizziness, nausea, and feeling faint.
Plus, because the "vast majority of women have never heard of a decidual cast," finding the fleshy mass in your underwear or in the toilet can be really disturbing, says Dr. Lee, who notes that many women assume they've had a miscarriage.
If you think you may have passed a decidual cast, Dr. Lee strongly advises you to see a doctor without delay. Either call 911, head to the emergency room, or get a same-day appointment with your GP or a local sexual health clinic.
While you wait, she also shares that you should:
- Do an at-home pregnancy test
- Take a simple pain reliever, such as ibuprofen or acetaminophen
- Continue to use your regular method of contraception
- Stay calm
"Once the tissue has been passed, the symptoms usually settle very quickly," Dr. Lee reassures. Though it might sound grim, she recommends taking the lump of tissue you passed to your appointment to show the doctor. "This can be sent to the pathology laboratory for analysis to confirm the diagnosis," she explains.
Does a decidual cast have links to endometriosis?
Endometriosis is a condition where tissue similar to that found inside the womb grows elsewhere in the body, causing scarring, pain, and other symptoms. And while there's no conclusive link, some people with endometriosis do experience decidual casts. While more research is needed, it's thought that those with endometriosis have an increased risk of an ectopic pregnancy, which can in turn lead to an increased risk of a decidual cast.
It's also thought that the formation of a decidual cast can be linked to hormone therapies or hormonal birth control, which many endo sufferers may take while searching for a treatment or pain management plan.
Some with endometriosis may also experience heavy periods, featuring clots of varying sizes, possibly due to hormonal imbalances.
This article is not intended to be a substitute for professional medical advice or diagnosis. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
Sophie Williams is a Freelance Journalist and Copywriter, covering everything from Fashion to Entertainment to music, Lifestyle and Features. She has interviewed a range of musical artists and authors including Alyssa Edwards, Courtney Barnett, Confidence Man, The Vaccines, Loyle Carner, Gabrielle, and John Niven, and has written for publications like Metro, Reader's Digest, ITV's Woo! and Vice’s NBGA. She is also working on a book for HarperCollins about Taylor Swift, due to be published in 2024.
