Ovarian Follicle Morphology Analysis

Paraffin-embedded ovaries were serially sectioned. The first section containing ovarian tissue was collected. Every six sections, another section was collected until 20 sections were collected. HE staining was performed to evaluate the morphology of follicles. The criteria for the classification of follicles are as follows: primordial follicle, the oocyte was enclosed by a layer of squamous granulosa cells; primary follicle, the oocyte was enclosed by cuboidal granulosa cells; secondary follicle, the oocyte was enclosed by 2 or more layers of granulosa cells; and antral follicle, an antrum cavity was present. We avoided recording the same follicle more than once.