A Prospective Pilot Study Comparing Fertilization and Embryo Development Between Fresh and Vitrified Sibling Oocytes

Objective: To evaluate the outcome of a newly established oocyte vitrification program in women undergoing in vitro fertilization (IVF) within a short timeframe by simultaneously evaluating embryos derived from vitrified and fresh oocytes from the same stimulated cycle.

Design: Cohort prospective controlled trial and case-control study.

Setting: University-based tertiary fertility center.

Patient(s): Fourteen women who fulfilled the inclusion criteria underwent controlled ovarian hyperstimulation and Intracytoplasmic sperm injection (ICSI) treatment.

Intervention(s): Oocyte vitrification.

Main Outcome Measure(s): The primary outcome measures were oocyte survival, fertilization and cleavage rate, and subsequent embryo development, compared between vitrified and fresh oocytes. Secondary outcomes were implantation, clinical pregnancy, miscarriage and live birth rates using embryos derived from the vitrified oocytes for transfer. This was compared with age-matched controls who met similar inclusion criteria as the study patients and who underwent IVF during the same time period. Neonatal data on all newborns was also collected.

Results: From October 2009 until November 2010, a total of 17 patients were enrolled in this study (mean age 31.9 +/- 2.9 years). Three subjects withdrew prior to retrieval and one subject did not have a transfer from vitrified oocytes. A total of 164 metaphase II (MII) oocytes were retrieved (mean 11.7 +/- 3.7), 83 were vitrified with 86.7% survival. Fertilization rate was similar between vitrified and fresh oocytes (69.4 vs 78.2%, P = 0.8). Cleavage on day two, however, was lowerin the vitrified oocytes (88% vs 100%, P = 0.004). Implantation rate (IR) was 25% (7/28) with a mean number of 2.0 +/- 0.5 embryos transferred. Live birth rate/embryo transfer (ET) was 46.1% (6/13) after transferring embryos derived only from vitrified oocytes, (six live births, seven babies,one set of twins). One additional ongoing pregnancy has been established after transfer of a cryopreserved blastocyst derived from a vitrified oocyte (combined pregnancy rate/ ET: 50%; 7/14).

Conclusions: This study provides a viable model to quickly assess the efficacy of a newly established egg vitrification program following American Society for Reproductive Medicine (ASRM) guidelines in an investigational protocol. Embryos resulting from oocyte vitrification resulted in optimal live birth and implantation rate. The lower cleavage rate noted in this study may indicate a possible detrimental effect of the vitrification process, which may be overcome with additional experience and refinement of the technique.