In vivo maturation of oocytes by extending the interval between human chorionic gonadotropin administration and oocyte retrieval

Objective: To find whether the percentage of mature oocytes can be increased in the following ICSI cycle, in a selected group of patients with ≥47% immature oocytes, with the prolongation of hCG-to-oocyte retrieval interval. Design: Randomized study. Setting: In vitro fertilization unit in a medical center in Israel. Patient(s): From January 2003 to June 2005, in 72 of 2,650 intracytoplasmic sperm injection cycles (2.8%), ≥47% of the total aspirated oocytes were immature (group A). In the following treatment cycle, with similar controlled ovarian hyperstimulation, hCG was planned to be injected in the same interval (group B) as well as 3-4 hours earlier (group C). In fact, the hCG-to-oocyte retrieval interval in group C was statistically significantly longer (38.6 ± 1.2 hours) compared with that in group B (35.3 ± 0.7 hours). Intervention(s): The clinical characteristics of the patients, ovarian stimulation, hormonal profile, and the intracytoplasmic sperm injection outcome of the various groups were assessed. Main Outcome Measure(s): The number and maturity of the aspirated oocytes. Result(s): The mean number of ampules needed for stimulation, treatment duration, serum E₂, and P level on the hCG day were similar in the various groups. Escaped ovulation did not occur in any of the patients. A larger number of aspirated oocytes, a statistically significantly larger percentage of mature oocytes (72%), and a statistically significantly lower percentage of metaphase I (12%), germinal vesicle (18%), and degenerated oocytes (8%) were found in group C compared with group A (50%; 16%, 21%, and 13%, respectively). Similar morphological distribution of the aspirated oocytes was observed among groups B and C. Clinical implantation and pregnancy rates were higher in group C compared with group B. Conclusion(s): In a selected group of patients with ≥47% immature oocytes per retrieval, a larger cohort of mature oocytes can be recruited by extending the hCG- to-oocyte retrieval interval in a subsequent cycle. This improved outcome directly affects the quality of embryos available for transfer and thus increases pregnancy rate.