THE RELATIONSHIP BETWEEN FOLLICLE SIZE, OOCYTE MATURATION, BLASTOCYST FORMATION, BLASTOCYST PLOIDY, AND PREGNANCY...

The relationship between follicle size, oocyte quality, and blastocyst ploidy is not fully established. This question becomes especially important for poor responders and older reproductive age women, where optimal follicle size and oocyte quantity cannot always be achieved during ovarian stimulation. The aim of this study is to determine the relationship between follicle size, oocyte maturation, blastocyst formation, blastocyst ploidy, and pregnancy outcomes in young women undergoing in vitro fertilization (IVF).

The study involved 32 oocyte donors aged 19 to 35. For ovarian stimulation, a protocol with GnRH-antagonists was used, employing downregulation with oral contraceptives. The ovulation trigger was administered when 20% of follicles reached 18 mm. Aspiration was performed 35 hours after the ovulation trigger was administered. Follicle size was measured immediately before the aspiration needle was inserted and follicle fluid was aspirated; data (follicle size and oocyte from this follicle) were recorded individually by the embryologist. The resulting blastocysts underwent preimplantation genetic testing for aneuploidy (PGT-A) using NGS. Pregnancy outcomes were assessed by biochemical indicators, miscarriages, and live births.

Out of 555 measured follicles, 508 oocytes were obtained (91.5%). The number of mature oocytes (MII) was 411 (80.9%), and there were 97 immature oocytes (19.2%). Out of the 97 immature oocytes, 51 were germinal vesicle (GV) oocytes (10.04%), and 46 (9.06%) were MI oocytes without a polar body. Follicles were divided into four groups based on size: Group I - <15 mm, Group II - 15-18 mm, Group III - 18-20 mm, Group IV - >20 mm. There were significantly more mature oocytes in the second, third, and fourth groups compared to the first, indicating that follicle size has a substantial impact on retrieving MII oocytes (p<0.0001). Especially high number of mature oocytes were observed in the second and third groups. Fertilization and blastocyst formation from oocytes obtained from larger follicles were higher than from smaller follicles (p<0.0001). The frequency of obtaining euploid blastocysts did not significantly differ between the groups, and no significant relationship was found between follicle size and the formation of euploid blastocysts. Women who underwent genetic testing of embryos and transferred euploid embryos had significantly lower rates of biochemical pregnancy and miscarriages, as well as significantly higher live birth rates compared to those who did not undergo genetic testing of embryos.

Oocyte maturation, fertilization, and blastocyst formation depend on follicle size. However, follicle size is not an indicator of blastocyst euploidy. Preimplantation genetic testing for aneuploidy (PGT-A) significantly increases pregnancy success and live birth rates while reducing miscarriage rates.