Vitrification

1. Oocyte Cryopreservation

Oocyte cryopreservation is the process of freezing and storing eggs for future use. It is commonly used for women undergoing medical treatments that may affect their fertility or those who wish to delay childbearing.

Procedure

1. Ovarian Stimulation:
   • Hormonal Treatment: Women receive hormonal medications (usually FSH and LH) to stimulate the ovaries to produce multiple eggs.
   • Monitoring: Ultrasound and blood tests monitor follicle development and hormone levels.
2. Egg Retrieval:
   • Procedure: Once eggs are mature, they are retrieved through a minor surgical procedure called transvaginal ultrasound-guided aspiration.
   • Anesthesia: Usually performed under sedation or general anesthesia.
3. Cryopreservation:
   • Preparation: The retrieved eggs are processed and evaluated for maturity.
   • Cryoprotectant Addition: Eggs are treated with cryoprotectants to protect them from ice crystal formation during freezing.
   • Freezing: Eggs are cooled using a slow-freezing method or vitrification (rapid freezing) and stored in liquid nitrogen at -196°C (-320°F).

Uses

• Fertility Preservation: For individuals undergoing treatments like chemotherapy or those delaying pregnancy.
• Egg Banking: For social or personal reasons, allowing women to store eggs for future use.

2. Embryo Cryopreservation

Embryo cryopreservation involves freezing embryos that have been created through in vitro fertilization (IVF) for future use. It allows couples to preserve embryos for future attempts at pregnancy or to use them if the initial IVF cycle is unsuccessful.

Procedure

1. IVF Process:
   • Stimulation and Retrieval: As with oocyte cryopreservation, the ovaries are stimulated, and eggs are retrieved.
   • Fertilization: Eggs are fertilized with sperm in the laboratory to create embryos.
2. Embryo Development:
   • Culturing: Embryos are cultured in the lab for several days, usually up to the blastocyst stage (day 5 or 6).
3. Cryopreservation:
   • Preparation: Embryos are evaluated for quality before freezing.
   • Cryoprotectant Addition: Embryos are treated with cryoprotectants to minimize ice crystal formation.
   • Freezing: Embryos are rapidly frozen using vitrification and stored in liquid nitrogen.

Uses

• Future Transfers: Frozen embryos can be used in future IVF cycles, reducing the need for repeated ovarian stimulation and egg retrieval.
• Fertility Preservation: For individuals or couples who wish to delay pregnancy.

3. Sperm Cryopreservation

Sperm cryopreservation involves freezing and storing sperm for future use. This method is used for fertility preservation in men undergoing medical treatments, those with certain medical conditions, or those who wish to store sperm before undergoing procedures like vasectomy.

Procedure

1. Sperm Collection:
   • Sample Collection: Sperm is typically collected through masturbation into a sterile container. If a patient is unable to provide a sample, sperm can also be collected surgically or through electroejaculation in certain cases.
2. Processing:
   • Evaluation: The sperm sample is analyzed for quality, including concentration, motility, and morphology.
   • Cryoprotectant Addition: Sperm is mixed with a cryoprotectant to prevent damage during freezing.
3. Cryopreservation:
   • Freezing: The sperm is gradually cooled and then rapidly frozen using vitrification. The samples are stored in liquid nitrogen.

Uses

• Fertility Preservation: For men undergoing treatments that could affect fertility or those planning to delay fatherhood.
• Donor Sperm: For use in assisted reproduction or donor sperm banks.

General Considerations for All Cryopreservation

• Thawing: Each type of cryopreserved material (oocytes, embryos, sperm) is thawed using specific protocols to ensure cell viability.
• Success Rates: Viability and success rates vary depending on the method used (vitrification vs. slow freezing), the quality of the samples, and individual factors.
• Storage: Samples are stored in liquid nitrogen, maintaining them at temperatures around -196°C (-320°F) to ensure long-term preservation.

Cryopreservation plays a crucial role in modern fertility treatments and preservation, providing valuable options for individuals and couples planning for future reproductive opportunities.