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Ultrasound:  High frequency sound waves used to provide images of tissues, organs and other internal bodily structures.

Ultrasound-guided aspiration:  A non-surgical, non-invasive method of egg recovery using ultrasound images to guide the path of the oocyte recovery needle.

Unstimulated cycle: No drugs are given to stimulate egg production.  Also known as a natural cycle. 

Uterus: The female womb in which the embryo develops.