Correlation of follicular diameter with oocyte recovery and maturity at the time of transvaginal follicular aspiration

Forty-four consecutive patients undergoing transvaginal follicular aspiration for in vitro fertilization underwent ultrasonic measurement of follicular diameter at the time of oocyte retrieval to determine the correlation of follicular size with recovery rates and oocyte maturity. Based on the results of 412 follicles aspirated, the data were grouped by size (≤11, 12-14, 15-17, 18-20, and ≥21 mm) and oocyte maturity. Recovery rates were significantly higher in 18- to 20-mm follicles (P<0.01) and lower in those ≤11 mm (P<0.001). The probability of retrieving a metaphase I or II oocyte was significantly lower in follicles ≤11 mm (P<0.001), somewhat higher in 12- to 14-mm follicles (P<0.01), and equally high among the other groups. There were no differences in the incidence of fractured zonas. We conclude that follicles ≥15 mm provide the highest probability of retrieving mature oocytes and the low recovery rates of mature oocytes from follicles ≤11 mm suggest that, in selected circumstances, the operating surgeon may choose not to aspirate them.