**1. Introduction**

Cryopreservation of human gametes and embryos is very important method in most embry‐ ology laboratories. Two basic cryopreservation techniques rule the field, slow‐rate freezing (first developed) and vitrification, which have gained a foothold in recent years. Vitrification is relatively simple, requires no expensive programmable freezing equipment and uses a small

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

amount of liquid nitrogen for freezing. Vitrification of human oocytes and embryos (especially at early stages) is more effective than slow freezing.

During last years, the practice of single embryo transfer was a greater demand for reliable cryostorage of surplus embryos. The first reports of successful freezing and thawing of human embryos were in 1983 [1]. There are a growing number of indications for oocyte cryopreser‐ vation as oocyte donation, fertility preservation for cancer patients or social egg freezing. Reproductive behaviour of women has been changed in last years. There is a delay in the age of motherhood due to various reasons like career, live style or education. It is known, that in women older than 35 years, reduction of ovarian reserve is observed. The use of younger cryopreserved oocytes can reduce the risk of foetal loss and aneuploidies associated with ageing oocytes. Oocyte cryopreservation simplifies the logistics of assisted reproductive technology (ART) cycles in donation programme, and there is no need for menstrual cycle synchronization between donor and recipient.

Damage of reproductive function is very frequent and well documented side effect associated with the treatment of malignant tumours. The increasing success of cancer treatment and determined efforts to improve the quality of life after successful treatment has turned attention to the preservation of reproductive function in young women and also in young men. Sperm freezing is largely recommended to preserve fertility prior to the oncology treatment. Cryo‐ preservation of spermatozoa is routinely used in a variety of reasons (sperm bank, donor programme, etc.).

For this reasons, cryopreservation of gametes and embryos is more and more important part of human‐assisted reproduction.
