Embryo Freezing

Embryo freezing involves in vitro fertilization, a procedure in which eggs are removed from a woman’s ovary and combined with sperm in the laboratory to form embryos. The embryos are frozen and can later be thawed and placed in a woman’s uterus. Embryo freezing is a type of fertility preservation. It may be useful for women with cancer who want to have children after having radiation therapy, chemotherapy, or certain types of surgery, which can cause infertility. Also called embryo banking and embryo cryopreservation. Embryo Freezing or Cryopreservation is generally performed as a component of infertility treatments like In Vitro Fertilization (IVF) and Intracytoplasmic Sperm Injection (ICSI). During a standard IVF or ICSI treatment cycle, hormones are used to stimulate the development of multiple eggs in a women’s ovary. Generally, for more than 50% of couples, there will be excellent quality embryos in addition to those that can be used for embryo transfer. 


The air that we breathe contains a gas called nitrogen. This gas makes up about 78% of the air around us. If nitrogen gas is cooled, it becomes liquid at -1960C. This liquid is very stable and easy to work with. In the laboratory we have large tanks filled with liquid nitrogen in which we store frozen embryos. Each tank is in effect like a large thermos flask since it is vacuum lined. All patients have designated storage spaces within a tank, where their eggs or embryos are kept. The straws that contain the embryos are color-coded and labeled with precise and unique identifying information.

The tanks that contain frozen embryos are monitored 7 days a week. Each tank gets a physical inspection daily, looking for problems or signs of problems. The quantity of nitrogen in the tank is assessed as a means of monitoring for a possible slow leak or an impending tank failure. The nitrogen in the tank is topped up daily, since it continuously evaporates at a slow rate.

Electronic tank monitoring uses different sensors to ensure that tanks perform to specifications. Probes attached to the tank detect a rise in temperature within the tank, or a drop in the level of liquid in the tank. Sensors are connected to a telephone alarm system that will alert staff to an alarm condition outside of normal working hours

The telephone alert system is a complicated monitoring device. It requires that multiple people be contactable at any given time, and calls and recalls each person in turn until somebody responds to the alarm. We aim to have an embryologist in the laboratory no more than 30 minutes (day or night) after the alarm is set off. The alarm system is tested weekly and continues to run on battery power in the event of a power failure. The alarm system can also be checked remotely. The status of each individual tank can be ascertained by telephone at any time.