functional ovarian cysts

Yes, ovarian cysts are expected!

Ovarian cysts are very common. In fact, 100% of normally functioning ovaries will have a cyst at some point!

Yes, I said 100%. Ovarian cysts ARE EXPECTED. 

Photo: Tachina Lee via Unsplash

Ovarian cysts can also be unexpected, or a sign of a health problem, or painful, or dangerous. To make ovarian cysts confusing, we always have to remember that some ovarian cysts are normal and go away on their own (most likely, and what this article is about), and some ovarian cysts can lead to death (less likely causes like ovarian cancer). 


That’s why ovarian cysts are evaluated and followed closely and sometime warrant surgery. 

Today we’re talking about those first types of cysts – the common, normal, expected cysts that signal healthy ovaries. 

These are physiologic, or functional, ovarian cysts. I like the term “functional cysts” because the cysts are doing just that – performing a function. 

Remember the menstrual cycle that I talk about incessantly? (If you need a refresher, read this article. Or, if you want to take a deep dive, get on the wait list for The Female Body course my partner and I are preparing because you just can’t get organized, in depth information anywhere else). 

Anyway …

Functional ovarian cysts are part of the menstrual cycle. 

In the first part of the menstrual cycle, the follicular phase, many eggs are recruited as potential ovulators that month. Each egg has its own follicle. As the eggs mature, the follicles get bigger – around 1 centimeter each. These follicles look like cysts on ultrasound – small fluid filled cysts. I prefer to call them follicles at this point because it’s a more accurate description. Only one of these eggs becomes the chosen one – the one to completely mature and ovulate that month. That egg’s follicle continues to grow until ovulation, to about 2 – 2.5 centimeters. This follicle is a functional cyst – its function is to hold the maturing egg. Sometimes this cyst is called a follicular cyst as well. What happens to the other follicles and eggs?  They regress, then dissolve. 

Ovulation occurs. The egg is released from this matured follicle (the follicular cyst). 

The follicle, now without the egg, turns into a corpus luteum, sometime called a corpus luteal cyst. This cyst secretes progesterone, prepping the uterine lining in case a pregnancy ensues. 

If no pregnancy, the corpus luteum dissolves. 

If a pregnancy does occur, the corpus luteum continues to secrete progesterone until the placenta is functional enough to take over that job (around 12 weeks, roughly). 

So you see – the function of this cyst is to secrete progesterone! It’s part of the normal, physiologic process of the menstrual cycle!

Can either of these functional cysts be problematic? 

Photo: Simran Soon via Unsplash

Yes, in 2 specific situations. 

  1. Fluid filled cyst. Some people are prone to anovulation (not ovulating) – the most common of these is polycystic ovarian syndrome. The follicles grow but the eggs never get to the point of ovulation. These follicles can get quite large and filled with fluid – up to the size of a baseball. This growth can cause some pain or discomfort as the ovary stretches but most of the time they go away on their own. 
  2. Bleeding (hemorrhagic) cyst. 

There are 2 leading theories as to how these cysts bleed. One is that the egg, at time of ovulation, may burst through a small artery or vein, causing it to bleed. The second theory is that the corpus luteum wall is delicate, and some sort of “trauma” (like heavy exercise or penile-vaginal intercourse) disturbs it and causes it to bleed. 

These hemorrhagic cysts are more common on the right side due to anatomy (the colon on the left side may help protect the left ovary) and it’s documented that 50% of the time, intercourse precedes the diagnosis. People with bleeding disorders or on blood thinners (even NSAIDs and aspirin count sometimes!) are at an increased risk. 

The good news is that the bleeding is often a small amount – a bit of blood accumulates in the corpus luteal cyst or around the ovary, sometimes even leaking into the abdomen. It can be uncomfortable and painful and sometimes even an emergency room evaluation is warranted. Most of the time though, the bleeding is self-limited, self-contained, and goes away in a week or so. If I see a type of cyst like this on ultrasound, I typically repeat the ultrasound about 6 weeks later (aka NOT around the time of ovulation) to make sure it resolved. 

Leave a Reply