A detailed view of the process of Cryopreservation

Cryopreservation ( known as freezing in lay terms ) is a procedure in which organs, embryos, tissues, cells or any such similar biological composes, are stored in liquid nitrogen at very low temperatures ( generally at -196°C). It is not simply cooling but primarily to preserve their viability. One of the major issues with cooling is the conversion of intracellular water into ice crystals leading to cell damage. This is minimized by using cryoprotectants during the process of freezing and thawing.

When is Cryopreservation done?

Cryopreservation of cells is an essential part of the in-vitro-fertilization (IVF) procedure. It is used for either Gametes [ haploid cells: sperms and eggs ] or for Embryos or for tissues [ Testis or Ovary ]. Embryo preservation is the most effective option today, but in unmarried/single persons, it is not an option.

What is sperm cryopreservation and who opts for it?

Semen freezing or sperm cryopreservation is the process of freezing human semen for future use. A man may opt for sperm cryopreservation for one or more of the following reasons:

  • If he runs a risk of low sperm count
  • If the quality of the sperm is deteriorating
  • If he has a condition or a disorder that could affect his fertility e.g. malignancy of the testes requiring surgical removal or other malignancies / autoimmune disorders requiring chemotherapy or radiation therapy
  • If he is about to get a vasectomy

It is observed that sperm tends to show a high survival rate in cryopreservation due to the low water content in it, which reduces the chance of ice formation. However, cellular damages aren’t completely unlikely upon semen freezing and/or thawing. One such frozen sample can be used generally only once, so to improve the chances of pregnancy, it is better to freeze multiple samples.

What is oocyte cryopreservation and who needs it?

Egg freezing or oocyte cryopreservation is the process of freezing fertilized eggs in order to preserve the vitality and quality of the egg for later use. A woman may opt for oocyte cryopreservation for one or more of the following reasons:

  • If she’s diagnosed with any condition e.g. malignancy, an autoimmune disorder that requires chemotherapy and/or pelvic radiations which can affect fertility
  • If she runs a risk of premature ovarian failure, due to diseases like endometriosis cyst of the ovary, or has a family history of early menopause
  • Personal choice of delaying childbearing [ in unmarried women ]

The success rate following oocyte cryopreservation and the ideal number of oocytes to be frozen depends on the age of the woman because the egg quality declines as the age advance esp after the age of 35 years.

What is Embryo Cryopreservation and who needs it?

It is normal in an IVF procedure to have more embryos than that will be put back in the uterus. These surplus good quality embryo preservation for:

  • Having a second pregnancy when the first attempt is successful
  • Having a second attempt if the first one fails

The embryo freezing process or the process of freezing fertilized eggs is much simpler, does not involve the use of multiple injections for stimulation of the ovaries, requires no anesthesia, and hence is significantly cheaper but equally successful.

How is cryopreservation done?

The process of cryopreservation is done by anyone of the following two freezing methods. In both, before freezing the cells, special fluids called the cryoprotective agents (CPAs) are added, with the purpose of removing the intracellular water and hence protect the cells during the freezing process.

 1. Vitrification

Vitrification is an ultra-fast freezing method of a liquid medium, in which the entire solution solidifies in less than one second. Vitrification is a procedure in the sperm/egg or embryo freezing process, in which the gametes are frozen so quickly that there is no time or scope for ice crystals to form. The main concern, in the process of cryopreservation, is the water within the cells. When the water gradually freezes, there is a chance of the formation of ice crystals, which results in bursting of cells. Vitrification eliminates the possibility of this and also increases the survival rate of the gametes upon thawing.

2. Slow Freezing:

While Vitrification was introduced in the mid-2000s, slow freezing is a more traditional and conventional method, that was first introduced in 1986. In the slow freezing process, the gametes/embryos are frozen in stages. CPAs are added to the cells in timed batches over 10-20 minutes. After this, the gametes are stored in a machine that lowers the temperature every minute, for over two hours. Upon reaching the freezing point, the gametes are stored in liquid nitrogen at -196° C.

    However, slow freezing is time-consuming and also requires expensive machinery. Furthermore, the slow freezing method does not wholly prevent ice crystal formation, therefore leading to a risk of cell damage or death.

According to research, vitrification has shown more chances of cell survival in both freezing, as well as the thawing process when compared to the slow freezing method.

Are there risks/side effects of Cryopreservation?

Slow freezing has been in practice for more than 30 years and Vitrification for around 10 years. Studies till now have not shown any major side effects to the mother or the child. In a small percentage of cases, the sperms/eggs or embryos may not fully survive the process of thawing and warming. In addition, a few women may exhibit minor side effects like Breast tenderness, Bloating, Mood swings, or Vaginal discharge due to the drugs used.

To conclude, cryopreservation of cells [ sperms and eggs ] and embryo preservation is widely used in couples having infertility of those wanting to preserve their fertility. So if you or someone you know struggles with fertility, or has developed a condition that can affect fertility in the future, gamete cryopreservation may be a good way to reduce the chances of infertility. Consult a doctor today, or book an appointment with Dr. Banker.

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