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 (less than or equal to 11, 12-14, 15-17, 18-20, and greater than or equal to 21 mm) and oocyte maturity. Recovery rates were significantly higher in 18- to 20-mm follicles (P less than 0.01) and lower in those less than or equal to 11 mm (P less than 0.001). The probability of retrieving a metaphase I or II oocyte was significantly lower in follicles less than or equal to 11 mm (P less than 0.001), somewhat higher in 12- to 14-mm follicles (P less than 0.01), and equally high among the other groups. There were no differences in the incidence of fractured zonas. We conclude that follicles greater than or equal to 15 mm provide the highest probability of retrieving mature oocytes and the low recovery rates of mature oocytes from follicles less than or equal to 11 mm suggest that, in selected circumstances, the operating surgeon may choose not to aspirate them.