EFS

Empty follicle syndrome or EFS is usually defined as a specific disease when oocytes are not retrieved from mature ovarian follicles with apparently normal follicular development and estradiol (female steroid sex hormone measured in the blood, produced especially within the follicles of female ovaries Estradiol appears necessary to maintain oocytes in the ovary.
During the menstrual cycle, estradiol produced by the growing follicle triggers, via a positive feedback system, the hypothalamic-pituitary events that lead to the luteinizing hormone surge, inducing ovulation.) levels. It was first described in 1986 (but the name “Empty follicle syndrome was mentioned the first time earlier — 1950-60).

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This condition is very difficult, because the oocytes don’t retrieve even after Controlled ovarian hyper stimulation (COH is a special technique meaning using some fertility medications to induce ovulation.) for an assisted reproductive technology (ART is a fertility treatment which helps to have a child in cases of some health problems which do not allow to conceive naturally.
Here belong: fertility medication, artificial insemination, IVF) cycle, despite repeated aspiration (procedure that aims to retrieve oocytes from the follicles. It is performed through the puncture of the ovary with a needle which is introduced through the vagina and guided inside the follicles using ultrasound vision) and flushing. Ultrasounds & estradiol levels which show many potential follicles also give no guarantees in this case.