Embryo freezing overview
- Embryo freezing is an established technology routinely performed in conjunction with IVF procedures. The purpose of embryo freezing is to enhance a couple’s fertility potential.
- Good quality embryos remaining after embryo transfer can be frozen and stored for a future pregnancy.
- Pregnancies rates achieved with fresh or frozen (vitrified) embryos are very similar, although frozen rates are slightly higher than when fresh embryos are used.
What is embryo freezing?
Embryo freezing, or embryo cryopreservation, is the process by which embryos are frozen for a pregnancy in the future. Eggs collected during an IVF cycle are fertilized using the partner’s or a donor’s sperm. The resulting embryos are cultured most often for 5-6 days in the IVF lab, allowing the embryo to develop to a blastocyst stage, which would normally occur in the uterus during natural reproduction.
One or two embryos may be transferred into the patient’s uterus (in what’s known as a fresh IVF cycle) and the remaining good quality embryos are frozen using a process called vitrification.
High concentrations of cryoprotective agents are used in the embryo vitrification process. The vitrification agents dehydrate and solidify the embryo before ice crystals have a chance to form (ice crystal formation in all cells is associated with a decrease in survival after thawing). After a brief exposure to vitrification solutions, the embryo is rapidly immersed in liquid nitrogen that brings the temperature of the embryo to –320 degrees Fahrenheit.
At this temperature, the viability (capability of surviving) of the embryo is suspended in time. All biological activity stops within the embryo, preventing changes such as cell growth or death. Cryopreservation provides longevity for an indefinite amount of time.
The Loma Linda University Center for Fertility has almost equal IVF success rates using fresh and frozen embryos, 58 and 52 percent respectively.
The cost of keeping embryos stored frozen at the Loma Linda University Center for Fertility & IVF is currently $200 per year for the first five years. Embryo storage costs are the sole responsibility of the patient and her partner. Insurance companies typically do not offer storage coverage benefits. At LLU Center for Fertility, frozen embryos are stored in a secure location within the clinic.
Who should consider embryo freezing?
All couples or individuals undergoing IVF treatment should consider freezing their spare embryos. Freezing extra embryos allows an opportunity for family building at some time in the future without having to undergo another egg retrieval process.
Risks & considerations of embryo freezing
Embryo cryopreservation is a safe process. Studies show that the risk of birth defects among children born via frozen embryos is the same as those in normal births.
However, some embryos may not survive the freezing and thawing process. Survival rates using vitrification and warming tend to be around 95 percent. The amount of time embryos can stay frozen and remain viable is unknown, but cryopreservation itself is considered to have no time limit.
Ethical issues related to freezing embryos may involve the issue of destroying unused frozen embryos after family building is complete. Our physicians would be happy to discuss your concerns with you and refer you to specialized fertility counselors who can help in considering this issue.
Benefits of embryo freezing
Medications taken to stimulate development of multiple eggs for egg retrieval may result in abnormal hormonal levels during an IVF treatment cycle. With embryo freezing itself, the freezing of all good quality embryos with embryo transfer in a subsequent cycle or cycles has been shown to result in an overall increase in pregnancy rate.
Additionally, the risk of having a multiple pregnancy (twins or more) is greatly reduced by placing one embryo in the uterus. With embryo freezing, remaining embryos can be stored for use in a later transfer cycle.
Certain medical or practical considerations may prevent embryo transfer during the treatment cycle. Embryo freezing can benefit those women who undergo IVF treatment and experience ovarian hyper stimulation syndrome (OHSS). OHSS is caused by a reaction to the fertility drugs used to stimulate the production of multiple eggs during the ovarian induction phase of IVF. OHSS can have uncomfortable side effects, including bloating, headache and hot flashes. Women who experience OHSS during IVF often freeze their embryos to be transferred in a subsequent cycle.