Cryopreservation success at a glance
- There are some risks of cryopreservation, including damage to the frozen sperm, oocytes, or embryos.
- The success rate of IVF and pregnancy depends on a number of factors including patient characteristics, treatment approaches, expertise of the staff and physicians, the lab, and patient population.
- Using frozen sperm, oocytes or embryos makes IVF necessary; however, there has been no significant evidence linking IVF to birth defects.
What are some drawbacks or dangers of freezing sperm, oocytes, or embryos?
- Sperm: One of the drawbacks of freezing/thawing sperm is that it could be associated with DNA damage. Freezing or thawing of sperm can lead to increase production of oxygen radicals or unstable molecules, which could damage membranes or protein structure. This can affect sperm motility, viability, or function.Up to three cycles of freezing and thawing can be performed without causing a level of risk of DNA fragmentation significantly higher than following a single cycle of freezing and thawing.
- Oocyte freezing with the traditional method of slow freezing is more difficult and it could damage or harden the outer lining of the oocyte (shell of the egg) known as zona pellucida. Under such circumstances, it is difficult for the sperm to penetrate and fertilize the egg. Therefore, intra cytoplasmic sperm injection (ICSI) is required to fertilize the egg, which is then transferred in the uterus. Oocytes are most vulnerable to damage during the thawing process.
- Embryos are also most vulnerable to damage during the thawing process rather than the freezing. Ice shards can form within the vial, which can pierce or kill the embryos. During thawing, water often rushes back into the cell at a faster rate than cryoprotective agents can leave. This can result in swelling and death of a few individual cells.
Death of a few cells within the embryo does not mean that the embryo is not viable, especially if we are dealing with a blastocyst which contains more than 100 cells.
What is the success rate of pregnancy?
The success rate of IVF and pregnancy depends on a number of factors including patient characteristics, treatment approaches, expertise of the staff and physicians, the lab, and patient population. It is also important to understand that pregnancy rates are not the same as live birth rates.
Average success rates after fresh embryo transfers in the USA:
- 42 percent of women under 35
- 32 percent of women age 35-37
- 22 percent of women age 38-40
- 12 percent of women age 41-42
- 4 percent of women over 42
Average success rates after transfers of frozen/thawed embryos (blastocysts) in the USA:
- 39 percent of women under 35
- 35 percent of women age 35-37
- 29 percent of women age 38-40
- 21 percent of women age 41-42
- 15 percent of women over 42
What is the recovery rate of frozen sperm or embryos?
As mentioned earlier, the recovery rate or survival of frozen sperm or embryos with slow freezing is about 50%. While, with vitrification the recovery rate or survival is close to 95%.
Are there increased chances of birth defects with IVF?
There have been several studies to determine a link between birth defects and IVF, but to this day there has been no significant evidence linking IVF to birth defects. The risk of birth defects associated with IVF is not much different from what would be expected in the general population. The major birth defects seen in babies born via IVF and/or ICSI included heart defects and malformations of the uro-genital tract. Majority of the defects are genetic rather than developmental.