Blastocyst & Embryo Freezing in IVF, Vitrification & Cryopreservation

Success Rates of Frozen Embryo Transfer, cryo shipping, vitrification process:

A short history lesson of cryoshipping and vitrification process.

Vitrified Human Blastocysts and Surrogacy pregnancy

In 1972 preimplantation mammalian embryos were first successfully cryopreserved. The method was very time consuming. Slow cooling was used (1 degree/min or less) to about -80 degrees Centigrade. Then the embryos were placed in liquid nitrogen.The embryos also needed to be thawed slowly and a cryoprotectant added and removed in many gradual steps. This was a lot of work.

The first reported pregnancy in humans from frozen embryos was in 1983.Research continues in this area and human embryo freezing and thawing protocols have improved tremendously over the past 25 years.

What is the difference between slow freezing and vitrification?

Patients who undergo IVF may have several eggs collected. The eggs are then fertilized with a sperm and checked for fertilization. Fertilized eggs are called embryos. A patient may have multiple high quality embryos eligible for embryo transfer back to the uterus. A certain number of embryos are chosen for embryo transfer, and the surplus of high quality embryos can be cryopreserved for future use.

Blastocyst & Embryo Freezing in IVF, Vitrification & Cryopreservation

Previously, embryos were cryopreserved using a slow freeze method. Embryos were run through different solutions of media to Storage of Cryopreserved embryos dehydrate the cells of water and replace it with cryoprotectant. Then the cryoprotected embryos were individually labeled and stored in cryopreservation straws, which were put in special freezers. These freezers slowly (-0.3 degrees Celsius per minute), cooled the embryos to -35 degrees Celsius using liquid nitrogen. They were then stored in liquid nitrogen (-196 degrees Celsius). At that extremely cold temperature, cellular activity is essentially brought to a halt, allowing the embryos to remain viable indefinitely.

When patients decide to use their cryopreserved embryos to try for a pregnancy, the embryos are removed from the liquid nitrogen, warmed and run through solutions of media to remove the cryoprotectant and rehydrate the cells with water. During cryopreservation, the formation of intracellular ice crystals can damage the cells of the embryo, decreasing future viability. Therefore, new methods were developed to improve cryopreservation techniques.

Vitrification-hook Recent technical advancement in the field of cryobiology has opened up various options for freezing gametes and embryos at different developmental stages. The tendency of the IVF world to switch over to natural cycle IVF and to elective single-embryo transfer has put cryotechnology in the forefront of IVF. Vitrification method is gaining popularity as the method of choice for gamete/embryo cryopreservation.

Vitrification is a new process for cryopreserving embryos. Through vitrification, the water molecules in an embryo are removed and replaced with a higher concentration of cryoprotectant than in the slow freeze method. The embryos are then plunged directly into liquid nitrogen. This drastic (-12,000 degrees Celsius per minute) freezing creates a glass transition temperature, commonly called a “glass” state, and the embryos are vitrified. This quick freezing reduces the chance for intercellular ice crystals to be formed, thus decreasing the degeneration of cells upon thawing for embryo transfer.

Many studies show survival rates of vitrified embryos to be far higher than survival rates of slow freeze embryos.

Till now, we have received frozen embryos from many countries and successfully transferred them into surrogate mothers. Most of these embryos were frozen by the slow freezing process. As vitrification is becoming popular as a method of choice for freezing gametes, we have started receiving vitrified embryos from world over. Our first case of cryoshipped, vitrified blastocyst transfer has resulted in a pregnancy.