You will be given a definition of a task first, then some input of the task.
Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Abstract: Four patients who had no oocytes retrieved during an IVF cycle were studied in an attempt to identify predictors of such an occurrence and suggestions for its cause. All 30 follicles aspirated in five cycles in these four women yielded no oocytes. One patient had two cycles that produced no eggs. The empty follicle syndrome may represent a new syndrome and a cause of infertility.
Output:
Adult