Cryopreservation

Embryo cryopreservation has revolutionized the assisted reproductive technology or ART scenario. The first pregnancy from cryopreserved embryo was reported in 1983. In following years rate of pregnancy through frozen or cryopreserved embryo, which was later thawed or defrosted to be used, has increased significantly. The pregnancy rate for IVF using frozen/thawed embryos is significantly high. We at Nurture Clinic offer embryo cryopreservation to help couples going through IVF cycles.

Cryopreservation or cryoconservation is a process where cells, whole tissues, or organs are stored at very low temperature for frozen to keep them viable for further use. Frozen cells, tissues or organs can be used later after thawing.

After establishment of pregnancy, it is up to the couple to keep remaining cryopreserved embryo frozen or discard or donate them. They may donate the embryos to other couple seeking out for embryo donation or donate if for research purpose.

 

Process of Cryopreservation of Human Embryo

Eggs are extracted from a woman’s ovary and are fertilized in the lab with her husband’s sperms. There may be development of large number of embryos after fertilization and embryo culture. Two to three embryos are transferred in the uterus in an IVF cycle. Excess good quality embryos are preserved by freezing or cryopreservation for use in subsequent cycles.

Embryos can be frozen at any stage between one-cell (one day old) to the blastocyst stage (5-6 days old). But freezing them at blastocyst stage minimizes the waste of freezing of excessive numbers of embryos and help to differentiate the most potentially viable embryos. In certain cases such as risk of ovarian hyper stimulation all potentially viable embryos are frozen to be used in subsequent cycle as it is not possible to transfer embryo in the current cycle. 

Embryos are preserved in cryoprotectant fluid ("anti-freeze" solution) at -196°C, in containers of liquid nitrogen. When there is a need to use frozen embryos they are thawed out at room temperature. All thawed embryos are hatched through assisted hatching before being transferred to the uterus.

 

Advantages of cryopreservation

  • Reduced risk of multiple pregnancies if there are a large number of good quality embryos available for transfer. Excess good quality embryos can be frozen or cryopreserved. 
  • Increase in pregnancy rates by using cryopreserved embryos after thawing them during spontaneous ovulatory cycles.  
  • It decreases the need of ovulation stimulating drugs.
  • Enables doctor to select best possibly viable embryo for transfer.

 

Risks and Limitations

  • There is no guarantee of establishing an IVF pregnancy using frozen thawed embryos.
  • The main risk associated with cryopreservation techniques is the possible loss of embryos to cryoinjury. Some healthy embryos may succumb to the stress of freezing & thawing.
  • Cryopreservation is an expensive affair.
  • Cryopreservation has potential risk of birth defects in children produced from frozen/thawed embryos, though studies have not shown any such risks. Risks of freezing and thawing embryos are not fully known as of now.
  • If a clinic has not fully equipped with advance technology of cryopreservation, there is a risk of dying of embryos.