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Freezing of human sperm, eggs, and embryos

Within the laboratory, at PFC we have a tissue bank where one freezes and stores oocytes (eggs), sperm as well as embryos for our patients. The bank has a full-time manager under the supervision of the lab director and is also licensed by the State of California. All tissues in the bank are stored frozen in liquid nitrogen at a given temperature of -1960C in vacuum-lined tanks that are rather computer-controlled as well as monitored 7 days a week with a dedicated alarm system. The embryologists are of course responsible for maintaining the bank and no other PFC employee has access.

How are frozen embryos stored and monitored?

The air that one breathes does contain a gas called nitrogen. This gas does makeup about 78% of the air around us. If nitrogen gas is indeed cooled, it does become liquid at -1960C. This liquid is indeed very stable and also easy to work with. In the laboratory, one has large tanks that are filled with liquid nitrogen in which one store frozen embryos. Each tank is in effect like a large thermos flask since it is indeed vacuum-lined. All patients do designate storage spaces within a tank, where their eggs or embryos are kept. The straws that do contain the embryos are color-coded and also labeled with precise as well as unique identifying information.

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

Electronic tank monitoring does use different sensors in order to ensure that tanks perform to specifications. Probes attached to the tank tend to 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 rather alert staff to an alarm condition outside of normal working hours

The telephone alert system is indeed a complicated monitoring device. It does require that multiple people can be contactable at any given time, and calls and recalls each person in turn until somebody responds to the alarm. One has to aim to have an embryologist in the laboratory, not more than 30 minutes (day or night) after the alarm is set off. The alarm system is tested weekly and does continue to run on battery power in the event of a power failure. The alarm system can also be checked out remotely. The status of each individual tank can be rather be ascertained by telephone at any time.

How long can embryos be stored?

No one actually knows what the maximum storage period might be. Procedures for human embryo freezing were indeed developed in 1984 and only went into widespread use in the late 1980s. This does mean that the longest time human embryo cryopreservation has been stored is 25-30 years and, typically, patients who have left embryos in storage for this long are not coming back for them. Some patients have indeed come back after 10-15 years and the embryos have been thawed successfully and have created healthy babies. Beyond this time frame, one does not know how long an embryo will remain viable, but it is also possible that kept in liquid nitrogen, an embryo may be viable indefinitely.

How are embryos thawed?

Thawing the embryos is considered to be simply a reversal of the freezing procedure.

Thawing does include our SurTransferTM protocol. When an embryologist does remove embryos from the freezer, a second embryologist is indeed required to witness the act, and verify the identity of the embryos before they can actually be thawed. Under no circumstances can alone embryologist be able to remove embryos from the freezer without another embryologist confirming correct identification.

The cryopreservation embryos that are coming out of the freezer (at –196°C) are warmed to body temperature in 2-3 seconds. This rapid thaw method does minimal damage to the embryo from ice that could form during warming. The embryologist has to actually remove the antifreeze from the embryo and then replace the water that was removed at the time of freezing. This is actually done by incubating the respective embryo in decreasing concentrations of the antifreeze, and also increasing concentrations of water. Over a period of 20 minutes, the embryo is rather stepped through different solutions, until finally the antifreeze is gone and all the water has been replaced.

The embryo can indeed be ready for transfer in as little as 40 minutes after leaving the freezer.

Ferty9 hospital has got second fertility and test tube baby center in Telangana.  We are also the best in India to give excellent successful pregnancies with frozen embryo transfer.


Team Ferty9

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