Not pregnant have cyst end of period sonographer says looks like a doughnut . says its luteal is this a benign cyst

Sounds like it: A luteal cyst is a type of benign cyst. The doctor who ordered your sonogram will be in a much better position for interpretation as they can review the images and the actual sonogram report

Probably: I don't know the reason for your ultrasound examination that discovered this cyst. To find out if this is a luteal cyst, no doubt you were advised to repeat the ultrasound. Because a benign luteal cyst originated from an ovulation, the repeat ultrasound should take place before ovulation, that is, near mid cycle. Also, luteal cysts usually have smooth walls and clear liquid content.