Ultrastructural analysis of human germinal vesicle-stage oocytes retrieved after conventional and mild ovarian stimulation

Immature oocytes are considered to be used as an alternative source of oocytes for ARTs1, in particul a major focus is given to germinal vesicle stage oocytes (GV) for infertile women without recourse to controled ovarian stimulation (COH) and for those who do not produce mature oocytes2. This study was aimed to describe and compare differences in ultrastructure and morphometry of exclusively fresh GVs obtained from two different ovarian stimulation protocols, in order to consider the ultrastructure of well-preserved organelles as indicator for the GVs quality preservation and appropriate selection for ARTs procedures. Fresh GVs were recovered from consenting donor women undergoing ARTs due to tubal or male infertility factors. Ovarian stimulation was achieved with two different gonadotropin releasing hormone protocols: Full stimulation-long GnRH agonist (Fs) protocol, and Mild stimulatio- GnRH antagonist (Ms) protocol. Oocyte retrieval was performed 34–36 h after ovulation. Oocytes were fixed and processed for standard preparative for transmission electron microscopy (TEM) observations3,4. Light microscopy showed that all fresh GVs were of good quality. Ultrastructural data by TEM and statistical data showed a roundish, central located nucleus in most of Fs and Ms oocytes, an increased number of mitochondria at Ms oocytes even though in both groups mitochondria often located in perinuclear position and sometimes associated to small vesicles (mitochondria-vesicle complexes), an increazed vacuolization to Fs oocytes than Ms and the vaculoes normally found close to the nucleus in both groups , cortical granules dispersed throughout the whole ooplasm, an intact and continuous zona pellucida and an abnormal distribution of small microvilli detected in both groups. In conclusion the qualitative and quantitative data obtained in this study on fresh human Fs and Ms GVs may show a variety of ultrastructural alterations, possibly related, at least in a part, to the applied COH protocol.