Casting for determinants of blastocyst yield and of rates of implantation and of pregnancy after blastocyst transfers.

Objective: To identify determinants of blastocyst yield, implantation rate, and pregnancy outcome.

Design: Retrospective analysis of outcomes of 1,653 cycles of IVF.

Setting: Private infertility clinic.

Patient(s): Couples presenting to an infertility clinic for IVF.

Intervention(s): None.

Main Outcome Measure(s): Blastocyst yield, implantation rate, and pregnancy.

Result(s): Of a broad array of potential determinants, only the total numbers of oocytes retrieved and properties of day 3 embryos were consistently predictive of blastocyst formation. Relative to numbers of oocytes fertilized by intracytoplasmic sperm injection (ICSI), yields of quality blastocysts were highest in cycles in which <10 oocytes were retrieved. Blastocyst yield was closely linearly correlated with average numbers of blastomeres in embryos on day 3. As oocyte yields rose, average grades and the implantation potential of the blastocysts selected for transfer increased by approximately 0.015 and 0.15%, respectively, for each additional oocyte. Independently, the implantation potential of blastocysts decreased 1.1% for each advancing year in age of the oocyte provider, and, for autologous transfers, uterine receptivity declined an additional 0.6% per year. Higher yields of blastocysts from cycles with high oocyte numbers afforded better selection of blastocysts for transfer, supporting higher overall implantation and pregnancy rates.

Conclusion(s): While the proportion of fertilized oocytes that progressed to quality blastocysts diminished as numbers of recovered oocytes rose, rates of implantation and pregnancy after transfer of the selected best blastocysts increased. The age of the oocyte provider and oocyte yields independently impacted blastocyst implantation potential and uterine receptivity after controlled ovarian hyperstimulation, ICSI, and blastocyst transfer.