Ovarian cysts are often seen in early scans and are usually simple cysts. Most disappear by 20 weeks, though not in your case.
They're not cancerous, but can be a problem if they grow big or cause symptoms. Your doctor will try to avoid operating on the cyst until after your baby is born, and instead will monitor it via extra scans.
If the cyst gets so big it prevents the baby's head from engaging in your pelvis, your doctor may insert a needle and drain it when you're close to your due date.
If this is successful, you should be able to give birth naturally.
Your doctor can remove the cyst via keyhole surgery a few months after your baby's born. However, if you need a C-section for another reason, doctors will be able to remove the cyst at the same time.