A blastocyst transfer is an embryo transfer which involves transferring one or more embryos that are at a very advanced stage of development, the so-called blastocyst stage. This is usually done on the fifth day after follicular aspiration.
After the doctor has removed the eggs from an ovary (follicular aspiration), they are fertilized in the laboratory. This is done either by normal in vitro fertilization (IVF) or by means of intracytoplasmic sperm injection (ICSI).
Immediately after fertilization, an egg starts to divide and develop into an embryo. The stages of development are as follows:
- the pronuclear stage on the first day (fertilized egg)
- the two to the four-cell stage on the second day
- the eight-cell stage on the third day
- the morula stage on the fourth day and
- the blastocyst stage on the fifth day
- The doctor usually inserts one or more embryos in the woman’s uterus two to three days after egg retrieval. This process is referred to as embryo transfer.
The embryos can also develop in an incubator up to the fifth day, i.e. the blastocyst stage, thanks to improved cell culture media (blastocyst culture). If the doctor transfers such developed embryos into the woman’s uterus, this is referred to as blastocyst transfer.
Cryopreservation is a process where cells, whole tissues or any other substances susceptible to damage caused by chemical reactivity or time are preserved by cooling to sub-zero temperature. Semen cryopreservation is a process to preserve sperm cells. Cryopreservation of tissues began with the freezing of Fowl sperms, which during the year 1957 was cryopreserved by a team of scientists in the UK. The process was applied to humans during 1950 with pregnancies obtained after insemination of frozen sperm. Cryopreservation of spermatozoa is at present, the most valuable and used way to preserve reproductive function in men undergoing gonadotoxic treatment such as chemo- or radiotherapies.1 In addition, sperm cryopreservation is increasingly used even in cases of other disorders, such as autoimmune diseases and myelodysplastic syndromes requiring treatments that may affect reproductive functions. Moreover, sperm cryopreservation is offered to patients with severe oligospermia or ejaculatory disorder for intracytoplasmic sperm injection (ICSI). Also, some non-malignant diseases such as diabetes and autoimmune disorders may lead to testicular damage, and cryopreservation is also advisable in these conditions.2 It can be a boon in the armed forces scenario, for the couples who are unable to stay together due to their field or ship recruitments.
Cryopreservation is known to have detrimental effects on sperm structure and function. Recovery of an optimal number of functionally intact spermatozoa from thawed samples has always been the main objective of semen cryopreservation technology.4 The principle involved is the prevention of intracellular ice crystal formation and optimal dehydration of the cells. For this, a large variety of glycerol and non – glycerol-based cryoprotectants have been used. Cryoprotectants act by decreasing the freezing point of a solution by increasing the number of salts and solutes present in the liquid phase of the sample, thereby decreasing ice formation within the spermatozoa.5
The human uterus is considered as the best natural incubator for inseminated semen samples. Therefore most of the clinicians believe in inseminating semen samples immediately after thawing. This is because they fear that if the sample is kept in the in vitro conditions for a long time, the sperms might lose their functional capacity. The purpose of this prospective study was to carry out computer-assisted semen analysis of the frozen sperm sample after thawing and predict their cryosurvival and evaluate the progressive motility recovery rate of the frozen spermatozoa 20 and 40 min post-thawing.