The Ability of Ultrasound to Determine the time for Harvesting Preovulatory Oocytes

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Abstract
To achieve fertilization in vitro, it would seem important to harvest the oocytes just before ovulation. Monitoring of follicular growth by repeated ultrasonic examinations has been suggested as a method for determining the time for harvesting preovulatory oocytes. To assess the usefulness of this new method, 90 women were studied in 3 groups. Two groups (n = 71) received ovarian stimulation with clomiphene citrate/hCG or hCG alone; 1 group (n = 19) was untreated. Each woman was examined with ultrasound 2-3 h before the operation, performed on day 14 of the menstrual cycle. Blood samples for progesterone analyses were obtained from day 11 to 17 of the menstrual cycle to determine ovulation day. In the unstimulated group, the operation did not coincide with the day of the progesterone rise in any of the women and no preovulatory oocytes were found. In the stimulated women, progesterone rise and operation day coincided in 42%; preovulatory oocytes were obtained in 45% of the women. Follicles aspirated on the day of the progesterone rise were, on average, largest in diameter (20 mm, range 14-28 mm) and volume (3.3 ml, range 1-8 ml). When the follicles were .gtoreq. 20 mm in diameter and the rise in progesterone occurred on the day of the operation, preovulatory oocytes were found in 63% of the women. If ultrasound failed to visualize follicles in an ovary, the chance of obtaining a preovulatory oocyte was 5.5%. False ultrasonic results were obtained in 29% of the women. In stimulated cycles, no improvement in the success rate of obtaining preovulatory oocytes would have been obtained if the operation day had been selected on the basis of 1 ultrasonic examination alone, compared with routine operation at midcycle. This lack of improvement was due to the wide range of the diameters of preovulatory follicles and to false results of the ultrasonic examinations. The optimum time for harvesting fertilizable oocytes cannot be determined by ultrasound alone.