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 ≥5.0 mL). 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 ≥1.0 mL 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 ≥1.0 mL 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, ≥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.