Hi!
Congratulations! Number(s) 3 and 4! The cyst could be a corpus luteum cyst which may shrink on its own. It could be a result of the follistim, and may shrink on its own.
It could be unrelated to the pregnancy, and may have been there prior to the pregnancy for who knows how long! It may NOT shrink on its own. There is not too much that you can do to reduce it. I don't think that limiting your activities will be of any benefit, although the pregnancy itself will slow you down a bit. You are at risk for torsion or twisting of the cyst. If that happens, you will experience fairly severe pain and will very likely need emergency surgery. The MOST common time for torsion to occur though is after delivery when the uterus shrinks rapidly. If you need a c-section (VERY likely with twins!) the cyst can be removed at the same time. I suspect that your doctor will try to watch the cyst carefully throughout the pregnancy, at least until the second trimester. If it does continue to enlarge or if it looks suspicious for malignancy, it may need to be removed while you are pregnant. I have removed lots of cysts in the second trimester, and usually everything goes well, though there is a risk of miscarriage with surgery.
If the cyst ruptures, you will probably have pain for a few days, and then it will go away on its own. It is unlikely that rupture will cause any problems for the babies.
Well this is a pretty long answer! I hope it helps! Good luck!
Dr B
Thank you so much for the thorough answer! I appreciate it!