Correlation between human follicular diameter and oocyte outcomes in an ICSI program

To determine the correlation between the follicular sizes and oocyte recovery, metaphase II oocyte recovery, fertilization rate and good embryo quality from mature and immature oocytes in an intracytoplasmic sperm injection (ICSI) program.

991 follicles obtained from 72 ICSI cycles were classified into three groups according to their diameters as measured by transvaginal ultrasound including group A (< 10 mm), group B (10-14 mm), and group C (> 14 mm). All obtained oocytes were classified according to their nuclear maturation: germinal vesicle (GV), metaphase I (MI) and metaphase II (MII). Mature oocytes underwent ICSI while immature oocytes were further cultured until maturity before ICSI was performed. The rates of fertilization and good quality embryos at day 3 were evaluated.

A progressive and significant increase in the rates of oocyte recovery and MII oocyte recovery were observed from group A follicles compared to the other groups (p < 0.001). The fertilization rate of mature and in vitro matured oocytes, as well as the rate of good quality embryos showed a tendency to increase from group A to group C follicles, but not significantly. The corresponding fertilization rates were 78 and 55.3% (p < 0.001) for mature and in vitro matured oocytes, respectively.

Collection of oocytes from small follicles, especially with a mean diameter less than 10 mm, and in vitro maturation of immature oocytes before fertilization may allow the total number of good quality and transferable embryos to be increased.