What Is Embryo Freezing Really Like?

Freezing an embryo, or a fertilized egg, lets you have children later in life. Here's what you need to know about the process.

IVF sperm injected into egg
Photo: Science Photo Library/Getty Images

To fight against their ticking biological clocks, some women freeze their eggs for a later date. But did you know that couples can freeze embryos (fertilized eggs) as well? Here’s what the embryo freezing process is really like.

Why Do People Freeze Embryos?

Women often freeze eggs because life gets in the way of the baby-making process – for example, they’d like to focus on their career or they haven’t found a long-term partner. Couples freeze embryos for these same general reasons.

It’s a known fact that egg quality and quantity decreases as a woman ages, especially after she turns 35 years old. Using frozen embryos lets women have healthy pregnancies later in life. And since the embryo contains younger eggs, there’s less risk of pregnancy complications.

Another reason to freeze embryos: “If a couple is having their first child through in vitro fertilization (IVF), they may decide create multiple embryos. They can freeze and save some of these embryos for later cycles,” says Lauren Roth, M.D. a board-certified ob-gyn and reproductive endocrinology and infertility specialist with Shady Grove Fertility.

Freezing Embryos vs. Freezing Eggs

The main difference between freezing eggs and freezing embryos: “whether the eggs are fertilized before or after they’re frozen and thawed,” says Josh Klein, M.D., co-founder and reproductive endocrinologist at Extend Fertility. When freezing embryos, you need to know the intended father, since his sperm fertilizes the eggs before freezing. On the other hand, you can freeze eggs without sperm (they’ll be fertilized once you undergo IVF). Freezing embryos also lets you know how many eggs were healthy enough to survive fertilization, says Dr. Klein.

So which one is right for you? Embryo freezing can be tough for single women, or women who don't currently have a partner, for the obvious fact that you need sperm to fertilize the egg, says Dr. Klein. (Note that you can also freeze embryos with donor sperm, though). In general, it's better for couples who know they want to procreate together, but baby-making is delayed because of illness, career, family issues, or other circumstances.

How Do You Freeze Embryos?

Freezing embryos is a multi-step process. We break it down here.

Egg Retrieval: A woman takes hormonal injections for 8-10 days, which allow multiple mature eggs to develop in her ovaries, according to Dr. Roth. (A woman normally releases one mature egg per ovulation cycle). Then she undergoes a short procedure to retrieve the eggs. The surgery requires twilight anesthesia, but it has minimal side effects.

Insemination: In order to become an embryo, the egg must be fertilized with sperm – either from a partner or a sperm donor. The insemination happens in a petri dish. Doctors usually allow the fertilized egg to develop for 5-7 days until it reaches the blastocyst stage.

How many retrieved embryos are viable to freeze? “This is based on the couple and their ages,” says Dr. Roth. “More embryos become blastocysts when the female is under 35 years old – usually about 50% of embryos. This number is a little lower in older couples.”

Genetic Testing: Couples can opt for preimplantation genetic diagnosis (PGD) to test embryos for genetic abnormalities, including cystic fibrosis, muscular dystrophy, Huntington’s disease, and more. It’s especially useful if one parent is a known carrier of a genetic condition, since PGD can prevent transferring it to your future child.

Embryo Freezing: The embryos first go through cryopreservation, which removes water from the cell and replaces it with cryoprotectant. Then the embryo is usually frozen through vitrification; this preserves the embryo without forming damaging ice crystals. The embryos are stored in liquid nitrogen. About 95% of embryos survive this freezing, says Extend Fertility, and they’ll be viable in a frozen state indefinitely.

In Vitro Fertilization (IVF): When a couple decides to conceive, the woman will undergo IVF. The embryo will be inserted directly into the uterus to hopefully form a pregnancy. Success rates of IVF vary based on age. However, it’s about 39.5 % successful for women under age 35, according to the Society for Assisted Reproductive Treatments (SART).

What If I Don’t Use the Embryos?

Some couples may not use their embryos for a few reasons: they break up, one partner dies, they decide against having kids, or they get pregnant naturally. In this case, they have a few options:

How Much Does It Cost to Freeze Embryos?

The cost of embryo freezing varies by region and clinic, but here are some expected costs:

Aspects of embryo freezing are sometimes covered by insurance. Check with your insurance provider for more information.

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