Dear mammaof3, An ultrasound is the test of choice to try to distinguish between a fluid-filled vs. solid area, however no test is perfect. A needle aspiration is a simple next step of confirming that this is a cyst, if they can aspirate fluid then it is a cyst. Considering how quickly this showed up, and the changes that can occur with pregnancy, increase the likelihood that is a cyst, but rather than assuming that, hopefully the needle biopsy will confirm this.