The association of follicular fluid volume with human oolemma stretchability during intracytoplasmic sperm injection

Objective: Oocyte degeneration often occurs after intracytoplasmic sperm injection (ICSI), and the risk factor is low-quality oocytes. The follicular fluid (FF) provides a crucial microenvironment for oocyte development. We investigated the relationships between the FF volume aspirated from individual follicles and oocyte retrieval, oocyte maturity, oolemma stretchability, fertilization, and development. Methods: This retrospective study included data obtained from 229 ICSI cycles. Ovarian stimulation was performed according to a gonadotropin-releasing hormone antagonist protocol. Each follicle was individually aspirated and divided into six groups according to FF volume ( < 1.0, 1.0 to < 2.0, 2.0 to < 3.0, 3.0 to < 4.0, 4.0 to < 5.0, and ${\geq}5.0mL$). Oolemma stretchability during ICSI was evaluated using a mechanical stimulus for oolemma penetration, that is, the stretchability was assessed by oolemma penetration with aspiration (high stretchability) or without aspiration (low stretchability). Results: Oocyte retrieval rates were significantly lower in the < 1.0 mL group than in the ${\geq}1.0mL$ groups (46.0% [86/187] vs. 67.5%-74.3% [172/255 to 124/167], respectively; p< 0.01). Low oolemma stretchability was significantly more common in the < 1.0 mL group than in the ${\geq}1.0mL$ groups during ICSI (22.0% [13/59] vs. 5.8%-9.4% [6/104 to 13/139], respectively; p= 0.018). There was a relationship between FF volume and oolemma stretchability. However, there were no significant differences in the rates of fertilization, cleavage, ${\geq}7$ cells at day 3, and blastocyst development among all groups. Conclusion: FF volume is potentially associated with the stretchability of metaphase II oolemma during ICSI. Regarding oolemma stretchability, ensuring a uniform follicular size during ovarian stimulation is crucial to obtain good-quality oocytes.