Embryo Freezing


Embryo freezing, also known as embryo cryopreservation, is a method used to freeze and store embryos for future use. An embryo is formed when an egg is fertilized by sperm. This technique assists individuals with fertility and reproductive planning.

Reasons for undergoing the procedure

Embryo freezing is a common step after fertility treatments like in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). These procedures fertilize eggs with sperm, often resulting in extra embryos. Freezing these embryos allows for their use at a later date under various circumstances:

  • Postponing or canceling implantation: If you decide not to implant the fertilized egg immediately.
  • Delaying IVF: Planning to undergo IVF at a later time.
  • Backup for fertility treatment: Having an option if initial fertility treatments are unsuccessful.
  • Donation: Choosing to donate unused embryos to other individuals or researchers instead of discarding them.

Embryo freezing also serves as a means of fertility preservation. Scenarios include:

  • Cancer treatment: Women or individuals designated female at birth (DFAB) may want to freeze fertilized eggs before starting chemotherapy or radiation therapy, which could impact fertility.
  • Transgender individuals: Transgender men might choose to freeze eggs or embryos before beginning hormone therapy or undergoing gender affirmation surgery.


Embryo freezing does not carry any health or congenital disability hazards for the ensuing pregnancies. Research on the results of frozen-thawed embryos really demonstrates reduced risk of perinatal mortality, low birth weight, growth limitation, and premature birth.

The following are the primary dangers of cryopreservation of embryos:

  • Unviable embryos that cannot be frozen.
  • Inability to conceive following thawing and implanting embryos.
  • Higher incidence of pregnancy-related illnesses such placenta accrete spectrum and preeclampsia.
  • Multiple births (twins or triplets) if more than one embryo is implanted.
  • Embryo damage sustained while freezing.

Before the procedure

To freeze embryos, you must grant authorization. You will receive consent paperwork from your doctor to read and sign. The documentation should provide information like this:

  • The quantity of embryos to be frozen.
  • The duration of storage (usually ten years).
  • What occurs at the end of the storage period.
  • What occurs if you pass away or get too sick to decide before the storage term expires.
  • The permissible uses of the embryos (e.g., exclusive use for your fertility treatments, donation to research, or adoption by another infertile couple).

You can also get assistance from your doctor in determining the optimal time to freeze one or more embryos. There are several stages at which freezing may occur:

  • Cleavage stage occurs when a single cell divides and multiplies to form between four to eight cells within approximately 72 hours.
  • Blastocyst stage occurs when a single cell divides and multiplies to form between 200 to 300 cells within a span of five to seven days.

During the procedure

Embryos can be frozen using two different techniques: vitrification and gradual freezing.

Fertility specialists will do the following during vitrification:

  • Introduce a cryoprotective agent (CPA) to the embryos. CPA is a liquid that functions similarly to antifreeze, shielding cells from ice crystal formation.
  • Submerge the embryos promptly into containers filled with liquid nitrogen at -321° Fahrenheit (-196.1° Celsius).

Although slow freezing is no longer as popular, some reproductive specialists may still employ it. In slow freezing, experts in infertility:

  • Apply lesser quantities of a Cryoprotective Agent (CPA) to the embryos than those employed in vitrification.
  • Place the embryos in a cooling device, gradually lowering the temperature over a period of approximately two hours.
  • Transfer the embryos from the cooling device and store them in tanks filled with liquid nitrogen at -321° Fahrenheit (-196.1° Celsius).

The embryos for each procedure are:

  • Stored in small straw-like containers.
  • Marked with specific details to indicate ownership.
  • Remarkably, embryos retain their biological age when frozen. For example, if frozen at age 35 and used at age 50, the embryo’s age remains unchanged.

After the procedure

If and when frozen embryos become necessary, a reproductive specialist will:

  • Remove the embryos from the nitrogen-filled liquid.
  • Permit them to gradually regain their typical temperature.
  • To get rid of the CPA, soak them.
  • Utilize the embryos as directed; for instance, place them within your uterus.


After being thawed, an embryo is implanted into a woman’s uterus through a process called frozen embryo transfer. While this procedure is generally successful, numerous factors influence its success rates, including:

  • The mother’s age at the time the egg was retrieved.
  • Previous outcomes of pregnancies and fertility treatments.
  • Presence of reproductive issues like fibroids, endometriosis, and uterine polyps.
  • Overall health of both parents.

Your doctor will help you understand how these variables can affect your chances of success.