I also had an ovarian cyst with my son, they just kept an eye on it to verify that it was only a cyst. My understanding of what causes them is this: When you ovulate and the egg is ejected from your ovary, there is something left behind in the ovary called the corpus luteum (yellow body). It's basically just the cells left that were around the egg itself, and this is what actually secretes the hormones to maintain pregnancy for the first few months. NORMALLY, when a pregnancy is not occuring, this body starts to deteriorate becoming the corpus albicons (white body) and then continues to break down until nothing is left. I know that sometimes in pregnancy, it doesn't deteriorate when it should, so I imagine that the same can happen after a normal ovulation not resulting in pregnancy. I can't say that I know of them preventing pregnancy, because they are a relatively normal occurance. You may want to ask your doctor to give an explaination as to why these might be occuring. I know for me, having some knowledge of what is going on in my body to cause the situation makes me feel better about it. Don't hesitate to do an internet search on the subject as well. There are a lot of good resources out there. WebMD is a good place to start. Good luck!