Passing a Decidual Cast

Periods can be fairly easy, passing some tissue at a time, or off can come the whole lining in one piece called a decidual cast. Here’s what you need to know:

1. Your uterine lining thickens and thins during the cycle, but it stays fairly thin. The lining of the uterus is only 6-8 mm thick at the time of the menstrual period, and it is shed gradually, a few cells at a time. The decidual cast is when the entire lining passes spontaneously. 

2. Shedding that lining tissue is a normal part of your period. Passing your uterine lining at once during your menstrual period is not uncommon, but it usually both uncomfortable, and alarming to some. But us women are designed to have some sort of periods  Or Not? We have to pass tissue each month. Or Not? Are they good for us? Or Not? Do we want them? Or Not? Is this something that is individual? Or Not? It’s a complex topic that I will be discussing a lot over my time in this blog

3. Track your menstrual cycles. So lets start with basics: How much do we bleed and what are we loosing, and just what was this that the patient passed? And another basic: track your periods, and use an app. Women are on average bleeding about 40 ml per period: 1.36 liquid oz for us Americans…hum, that doesn’t sound like much, what the heck, but up to double that is normal. And yes, blood is mostly water, our circulating blood is about 90% water, our menstrual blood, it’s probably more dehydrated than that, and depending on the pace of our bleeding it could be much more dehydrated than that, and it is mixed with the tissue you see above although most cycles your tissue from your period passed in fragments.

4. Knowing when the tissue is actually a miscarriage. Most women confuse decidual tissue with a miscarriage. In a pregnancy, even a current miscarriage, your pregnancy test should be positive. And yes, that is menstrual tissue in our picture, the “decidua” is a type of lining, really a word given to the lining that is very progestegenic due to a pregnancy, but the cast picked up that name. Passing a decidual cast is not a pregnancy, but 5% of all cases of decidual cast are due to a tubal pregnancy, and very few are passed in pregnancy, before the fetus is formed, but the pregnancy is miscarrying. If you have something that is roughly an elongated egg shape and made of tissue that you pass then most likely it’s going to be your complete menstrual cycle, all of it. 

5. Menstrual cramps intensify when you pass a decidual cast. While there can be intense cramping, and even fairly heavy bleeding when you pass a decidual cast, there no positive pregnancy test.

6. Gynos will see decidual casts fairly regularly. Well, this patient tends to do this commonly (often, unfortunately, she doesn’t like seeing this), passes the whole uterine at once during her periods, although for most, if it ever happens to you it won’t happen again. 

7. Abnormally thick linings make passing a decidual cast more likely. In every menstrual cycle we renew our uterus by passing all the tissue of the lining. And if we have a fair amount or endometrial thickening, we do need to pass that extra amount as well, so it may be a bit more likely to have a decidual cast. So in some cases we need that period to pass that tissue. In other cases, we won’t have tissue to pass: maybe we are very young, very stressed, very low in estrogen (breastfeeding or training for a marathon), very old. Just a few cases where there is recurrent passing of decidual casts, there is a lot of discomfort, and this has been termed “membranous dysmenorrhea.” 
 8. Collect the tissue for inspection if possible. Bring the tissue to your gyno to check, but most likely you will not need any further testing to figure out what is going on. Your gyno can determine if you do need a check on hormones, contraception, or other conditions. Clean jar is all that is necessary. The tissue can be sent for analysis.SXLLM