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Embryo Freezing

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in Fertility Care

Embryo freezing, also called embryo cryopreservation, is a fertility preservation method where fertilized eggs (embryos) are frozen and stored for future use.
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Embryo Freezing

What is Embryo Freezing ?

Embryo freezing, also called embryo cryopreservation, is a fertility preservation method where fertilized eggs (embryos) are frozen and stored for future use. Unlike egg freezing, which preserves unfertilized oocytes, embryo freezing involves eggs that have already been fertilized with sperm and developed to an early stage (usually day 3 cleavage stage or day 5–6 blastocyst stage).
Later, these embryos can be thawed and transferred into the uterus, giving couples or individuals a chance at pregnancy even years after the embryos were created.
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Causes

Embryo freezing is done for both medical and personal/social reasons:

Medical Reasons:

  • Women undergoing cancer treatments (chemotherapy, radiation, ovarian surgery) that could damage ovarian function.
  • Couples going through IVF cycles who have more viable embryos than can be safely transferred at once.
  • Women with endometriosis, ovarian insufficiency, or risk of premature menopause.
  • To prevent waste of extra embryos created during IVF.
  • For patients with conditions requiring medical or surgical treatment that may affect fertility.

Personal/Social Reasons

  • Couples who are not ready to start a family immediately but want to preserve embryos for the future.
  • Delaying childbearing while securing higher-quality embryos at a younger age.
  • For couples undergoing IVF, freezing prevents repeated egg retrieval cycles if pregnancy fails the first time.
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When it is Considered ?

  • During IVF treatment when more embryos are available than can be transferred in one cycle.
  • Before cancer therapy or other fertility-damaging treatments.
  • For elective fertility preservation when couples wish to delay parenthood.
  • In cases of uterine or medical complications that make immediate embryo transfer unsafe (e.g., ovarian hyperstimulation syndrome or uterine polyps).

Types of Embryo Freezing

Slow Freezing (Traditional method)

  • Embryos cooled gradually.
  • Higher chance of ice crystal formation, which may damage cells.
  • Less commonly used today.

Vitrification (Modern Standard)

  • Ultra-rapid cooling with cryoprotectants.
  • Prevents ice crystal formation.
  • Ensures much higher survival rates upon thawing.

Step Process

Procedure

Step 1 : Ovarian Stimulation & Egg Retrieval
  • The woman undergoes ovarian stimulation with hormones.
  • Eggs retrieved via ultrasound-guided aspiration.
  • Eggs fertilized with sperm through IVF (in vitro fertilization) or ICSI (intracytoplasmic sperm injection).
  • Fertilization is confirmed, and embryos begin to grow.
  • Embryos cultured in a lab for 3–6 days.
  • They are assessed for quality (cell number, fragmentation, growth pattern).
  • Usually frozen at Day 3 (cleavage stage) or Day 5–6 (blastocyst stage).
  • High-quality embryos chosen.
  • Preserved using vitrification.
  • Stored in liquid nitrogen at –196°C.
  • Embryos can remain frozen for many years with minimal deterioration.
  • Legal storage duration may vary by country/clinic regulations.
  • When pregnancy is desired, embryos are thawed.
  • Transferred into the woman’s uterus during a natural or hormonally prepared cycle.
  • Any remaining embryos can stay frozen for later attempts.
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Benefits

  • Higher Success Rates than Egg Freezing : Embryos are more resilient to freezing and thawing compared to eggs.
  • Fewer IVF Cycles Needed : Couples can use frozen embryos from one egg retrieval cycle across multiple attempts.
  • Preserves Fertility Before Cancer Treatment : Protects against infertility caused by medical interventions.
  • Flexibility in Family Planning : Allows couples to plan pregnancy timing.
  • Avoids Wasting Surplus Embryos : Extra embryos created in IVF are stored rather than discarded.

Results & Success Rates

  • Survival Rate: 90–95% of embryos survive thawing with vitrification.
  • Implantation & Pregnancy Rates: Comparable to or even higher than fresh embryo transfer in some studies.
  • Live Birth Rates: Strongly depend on the age of the woman when eggs were retrieved and embryos created:
  • <35 years: Higher live birth rates.
  • 35–40 years: Moderate success.
  • >40 years: Lower success due to egg quality.
  • Frozen vs. Fresh Transfers: Frozen embryo transfers often result in lower risks of ovarian hyperstimulation syndrome and sometimes show better endometrial receptivity.
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