Laser surgery and cauterization are considered to be far less effective and only burn the top layer of endometrial tissue, allowing for the endometrioma and endometriosis to grow back quickly. Likewise, endometrioma drainage or sclerotherapy are somewhat controversial technique for removing endometriomas with varied degrees of success. Conservative surgery can be performed to preserve fertility in younger patients but as earlier stated can have the effect of raising FSH values and making the ovaries less productive, especially if functional ovarian tissue is removed in the surgical process.[citation needed]