as rufalina has told you...

every time you make and egg (which is usually every month), the follicle grows bigger and and bigger and then bursts to release the egg......

it then is called a corpus luteum and then it shrinks and goes away

sometimes the corpus luteum can hang around awhile and maybe fill up with a bit of fluid but they are generally harmless and eventually go away

sometimes if they don't go away and grow (I have had this a few times), they just do this tiny little op thru your belly button and pop it like a balloon.

in your case, being pregnant and not making any more follicles in your ovary for a while, you won't even notice it and by the time you give birth and get around to releasing more eggs, I reckon that corpus luteum will be long gone....