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19th Apr 2024

What is a decidual cast? Explaining the period phenomenon

Anna Martin

Decidual Cast?

A decidual cast may sound like a type of tree but it’s not

In fact, it is far from anything to do with foliage but it has everything to do with periods.

You may have heard of decidual casts thanks to people sharing their stories of experiencing one for the first time on their TikTok accounts.

Though they may sound scary – it has been a shock for those who had never heard of the phenomenon before it happened to them – they’re perfectly normal.

Here is everything you need to know about them.

What is a decidual cast?

A decidual cast is a large, intact piece of tissue that you pass through your vagina in one solid piece.

Once the tissue is outside your body, you may notice that it looks like the shape of your uterus.

It happens when the thick mucus lining of the uterus, called the decidua, sheds in the near exact shape of your uterine cavity, creating a triangular cast.

The medical term that doctors use for this is membranous dysmenorrhea and it typically happens during your period.

In adults, a uterus is about three inches long and two inches wide. That’s about the size a decidual cast would be too.

What causes it?

Decidual Cast
Credit: Canva

As there are so few documented cases of decidual casts, experts aren’t entirely sure what causes them.

Though according to Health there are several theories as to what may cause them.

Some experts have theorised that big changes in hormones – specifically, an increase in both estrogen and progesterone – might cause the spontaneous expelling of the uterine lining.

Abnormalities in the production of prostaglandin, a hormone-like substance, may contribute to a decidual cast.

On top of this, It’s believed that endometrial (uterine) infections and ectopic pregnancies may trigger a decidual cast, too.

Is there anything I should be concerned about?

Though it may be scary and painful you should have nothing to worry about after passing a decidual cast.

According to Healthline, it’s rare that a person should experience this condition more than once so it’s more than likely just a one-and-done.

Though if you have any concerns you should contact your doctor to rule out any other possible conditions.