The process of embryo freezing begins in the same way as an in vitro fertilization cycle: a female patient is usually placed on a course of ovary-stimulating medications to prompt her body to produce multiple eggs in one cycle. The patient is monitored over a period of 8–11 days with ultrasounds and blood work. Then, when the eggs are sufficiently mature, they are retrieved from the patient’s ovaries in a brief surgical procedure during which she is placed under sedation.
The sperm from the male patient or a sperm donor is prepared through a process called “sperm washing,” which isolates healthy sperm from the remainder of the seminal fluid in order to improve chances of fertilization. The sperm is then combined with the egg in the laboratory under careful observation to promote fertilization. In some cases, the doctors may recommend a procedure called intracytoplasmic sperm injection, or ICSI, in which a single sperm is injected directly into the egg.
After the eggs are fertilized to create one or more embryo(s), they are incubated in a specialized, finely tuned environment in the lab for 5–6 days, during which the embryologists monitor and support them to ensure they are developing properly. Then, the embryos—either all embryos, or just additional embryos not used in an IVF cycle—will be flash frozen in a process called “vitrification.” Vitrification cools cells so quickly (to a temperature of -196º Celsius, or about -320º Fahrenheit) that they become “glass-like,” or “vitrified,” minimizing the chance that the water inside the cells will form damaging ice crystals.
Embryo freezing is a highly effective and safe procedure. Typically, >/= 95% of embryos survive the freezing and thawing process, and studies indicate that frozen/thawed embryos have at least the same likelihood of resulting in pregnancy as “fresh” embryos transferred immediately. Recent data actually suggests that, all else being equal, an embryo transferred after freezing/thawing may actually be more likely to implant than an embryo transferred “fresh”.