I am not a doctor, but both my daughter and I have had surgeries to remove
ovarian cysts (different
types) removed within the past 2 months. From what I understand, 3.1 cm is moderately small, and the fact that it has fluid is also a positive sign that it may be a simple, follicular cyst. I believe that these types of cysts are fairly common, occur with the normal process of ovulation, are usually benign, and often disappear on their own or stop growing on their own.