Use of the LANDA Embryo Freezing Technique to Validate Frozen Embryo Transfer Success Rates

Over the past several decades, considerable effort has been expended toward the successful cryopreservation of various human cells. While attempts at cryopreservation have been directed at different tissue types, one of the most vigorously pursued targets has been reproductive tissue. Historically, cryopreservation of human sperm has existed for several decades. The earliest reports of pregnancies (Trounson et al., 1983) and births (Zeilmaker et al., 1984) from the cryopreservation of human embryos occurred in the early 1980s. Presently, the freezing and storage of human embryos following in vitro fertilization (IVF) is standard practice at most fertility clinics. In 2003, the CDC Assisted Reproductive Technology success rates report stated that 4,246 live births occurred out of 17,517 non-donor frozen embryo cycles.

Embryo cryopreservation has been a routine component of clinical IVF programs for more than 2 decades but has a relatively poor outcome in terms of post-thaw survival and pregnancy rates in a majority of IVF programs. Efficient embryo cryopreservation has several advantages. It helps to reduce costs and increases cumulative pregnancy rates. It can also help in cases of IVF cycles where embryos are not transferred due to ovarian hyper stimulation syndrome. It is also useful when technical difficulties are encountered at the time of an embryo transfer procedure.

One of the major concerns in IVF is high-order multiple pregnancies, which result from the transfer of multiple embryos in a given cycle. In the last 5 years, improved stimulation protocols, advances in culture and laboratory systems, and better identification of viable embryos have enhanced the success rates of IVF. During the same period, some clinics have started the practice of transferring two embryos to reduce multiple pregnancy rates without compromising overall pregnancy rates.

Furthermore, in recent years some European countries, particularly the Scandinavian countries, have taken a lead in performing elective single-embryo transfers and have achieved acceptable pregnancy rates. This trend is spreading to other countries. This can result in surplus embryos being available for freezing. With the application of ICSI, even patients aged 40 years or older may have embryos to freeze.

Review of the current literature reveals modest post-thaw embryo survival, implantation, and pregnancy rates. Post-thaw survival rates vary from 50% to 80% for different embryo stages. Implantation and pregnancy rates have varied from 3% to 15% and 15% to 25% respectively, which is approximately half of the rates achieved for fresh embryo transfers.