Embryo Freezing: Everything You Need To Know

Embryo Freezing:
Everything You Need To Know

A comprehensive guide to help you determine if freezing embryos is right for you.

An Introduction to embryo freezing

We've written this guide to help you understand the pros and cons of embryo freezing vs egg freezing, so that you can decide whether freezing embryos might be right for you.

We're finally starting to see assisted reproductive technologies becoming mainstream. While many people have heard of egg freezing, a large portion of the women we speak to at Lilia aren't aware that embryo freezing is an option.

What is a frozen embryo?

An egg, or an oocyte, becomes an embryo once sperm has fertilized it. When the gametes (sperm and egg) first fuse, this forms a single cell called a zygote.

Once this zygote undergoes cell division, it becomes an embryo. In an embryo, cells divide rapidly by multiples of two.

An embryo can be frozen at any time along the developmental trajectory until it reaches the blastocyst.

Up until this blastocyst stage, an embryo is a small cluster of cells that have not yet developed into a fetus or baby. We've included a diagram below outlining the different stages of embryo development.

The embryo freezing process

The process for freezing an embryo is much the same as freezing eggs, with a few extra steps required to fertilize the eggs you extract.

Step 1: Ovarian Stimulation

The first step here is to have your ovarian reserve and reproductive hormones tested with a blood test. The blood test primarily assesses your anti-müllerian hormone (AMH) levels and checks for any infectious diseases.

Knowing your AMH levels allows your physician to determine the best course of action to stimulate the development of many follicles in your ovaries. These follicles support the growth of mature eggs or oocytes.

Following this, the process generally involves 10-14 days of synthetic hormone injections. During the hormone treatment, you are monitored by physicians for any side effects of the hormone stimulation and to watch the follicles develop in your ovaries.

Step 2: Egg Retrieval

Once there are enough mature follicles, there is a quick out-patient surgical procedure. You are placed under a light anesthetic for the egg collection procedure.

A physician extracts the mature eggs from your ovaries using a vaginal ultrasound and a small needle to suction out the developed eggs. The recovery time for this process is typically just a few days. The operation itself is minimally invasive and as such you can expect to be back to normal within about a week.

Step 3: Fertilization and Freezing

The unfertilized eggs are then taken to a laboratory for an embryologist to fertilize them via in vitro fertilization (IVF).

For this to happen, the fertility specialist will mix unfertilized eggs with either sperm from a partner or a donor. If you are interested in learning more about donor sperm, fertility clinics in your neighborhood would be able to make recommendations about donor sperm, as most clinics have a sperm bank.

After observing that an egg has indeed been successfully fertilized, the embryo will be left at optimal conditions to develop for a few days before being frozen.

At this point, your embryologist will  leverage the clinic's chosen freezing method to preserve the embryos until you're ready to use them.
Embryo Freezing Model Alyssa

Does embryo freezing work?

The success rate of thawing frozen embryos is about 90%, meaning that most of the frozen embryos you freeze will be viable for transfer.

When you do eventually tha an embryo, the average transfer will result in pregnancy 50% of the time (via Society for Assisted Reproductive Technologies).

As such, if you are able to thaw and attempt to transfer 4 embryos, your expected odds of success are 94%. This is notably higher than the success rate observed with non-fertilized frozen eggs, where on average it takes 20 frozen eggs to approach 90% odds of success.

Unfortunately, the SART data sets do not report on the success of all embryo freezing and subsequent embryo transfers – so these data are not perfect.  Your personal fertility profile has a lot to do with the sort of success rates you can expect.

On top of this, each clinic has its own average rate of success, which can vary quite drastically. If you'd like hand finding the ideal fertility clinic, based on both patient reviews and transfer success rates, Lilia can help.

Embryo freezing legal considerations

One major difference between egg freezing and embryo freezing is that embryo freezing comes with material legal implications.

If you are a single woman freezing embryos you have created with donor sperm, you don't have much to worry about in this realm.

However, embryos formed from two consenting partners exist in a weird grey zone legally – sitting somewhere between a living being and shared property. 

Obtaining Consent

At the beginning of the embryo freezing process, both participants must provide consent on a variety of things.

The consent forms include the general conditions for the use of the embryo. They might also include the amount of time you plan to store the embryos and whether the clinic can donate the embryos after this time is surpassed.

Further, two of you will need to agree on who can keep the embryos in the event of a split between partners, or one partner's death. 

For an embryo to be used, both parties that have contributed to the embryo must have gone through this initial consent process.

Withdrawing Consent

Now here's the kicker: either party contributing to the embryo (sperm or egg) can withdraw their consent at any point up until the embryo is transferred to the uterus.

Suppose you and a partner form an embryo and one of you decides that you no longer want to use those embryos. In that case, neither of you can legally use any of these embryos.

For this reason, our team at Lilia often recommends that women freezing embryos also freeze a portion of eggs without fertilizing them, so as to keep their options open.

Following a split, many clinics will observe a one-year cooling-off period. During this period, the clinic will continue to store your embryos in case the withdrawing party changes their mind. 

In the case of a partner passing, typically the initial terms of your consent will dictate how embryos can be used. However, the specifics here vary greatly by geography. If you'd like, Lilia can help share more information regarding the laws surrounding these processes for your specific zip code.

Legal support

Upon beginning embryo freezing, your reproductive endocrinologist will help you navigate the appropriate consent forms and set you up with a lawyer specializing in these sorts of agreements before undergoing the process.

One item you will want to be sure to include here is who the child's legal parents or guardians will be following successful pregnancy and birth.

Given the legal complexity inherent to freezing embryos, you'll want to ensure you're working with a clinic you trust deeply. If you'd like extra support or recommendations, our team at Lilia can run you through our recommended legal checklist for embryo freezing.

How much does it cost to freeze embryos?

If you are to freeze your own fertilized egg with sperm from a partner, embryo freezing typically costs between $20,000 and $25,000. With Lilia though, you can do secure embryos for only $15,580 as we've negotiated discounts with clinics and medication providers on your behalf.

O embryos is as follows:

Oocyte collection:
The process of stimulating the ovaries with medication and fertility specialists costs about $12,000-19,000 for the first cycle and about $5000 for each additional cycle.

Alternatively, Egg donor: Depending on your location, the cost of egg donation can add to your total for this process. The cost of a donor egg can be anywhere from $25,000-30,000. 

Sperm donor (if required): Buying donor sperm costs anywhere from $200-3,000 per sperm sample.

The storage fees for embryos range from about $350 to $1000 per year. 

Embryo Transfer: This process typically costs about $3000-5000 per transfer. 

Keep in mind that some insurance companies will cover some of this cost.

Egg Freezing vs. Embryo Freezing

The egg and embryo freezing processes have a lot of overlap; the main differentiation is when the egg is fertilized. With egg freezing, the egg is fertilized only after it has been frozen and then thawed, often years later.

For embryo freezing, the egg is fertilized before freezing. The timeline for both processes and the majority of the costs are almost the same. 

On average, embryo freezing has a far higher cryopreservation success rate, due to their unique structure.

Embryos are made up of smaller cells with much less water inside. As such, there is a far lower risk of damage due to ice crystallization during the freezing process, improving overall success rates. 

There are some ethical considerations for egg vs. embryo freezing, though, as some people view the beginning of life at the time of fertilization. Many with this belief will instead opt to freeze their eggs.

Does freezing damage embryos?

Freezing embryos does occasionally cause damage, and sometimes the embryo may not survive the freezing process.

The success rate of freezing and thawing embryos hovers around 95% depending on the clinic.

That said, the embryos that do survive the transfer process have not been damaged. A clinic would not risk transferring a damaged embryo. No existing data suggest that frozen embryos are any different from embryos that have not been frozen.

What happens when you freeze embryos?

The process for embryo preservation is relatively simple in the laboratory. The process begins with egg collection after ovary stimulation, which is followed quickly by in-vitro fertilization of the eggs by an embryologist.

Here, your clinic will incubate high quality motile sperm with the eggs. You can monitor this process under a microscope and see when sperm penetrate the egg. The fertilized embryo can then be kept (using cell culture methods) for different lengths of time: 1 day for a zygote, 2-4 days for a 2-4 cell embryo, or 5-6 days for a blastocyst. 

At each stage of embryo development, the clinic you have selected can determine which embryos are the best for freezing.

Each clinic has standards and cut-offs for optimal embryo selection. These standards for embryo selection and freezing ultimately dictate the likelihood of pregnancy after embryo transfer. The higher the quality of the embryo during freezing, the higher the likelihood of pregnancy.

After selection, embryos are frozen to extreme sub-zero temperatures. Clinics freeze embryos either by using slow cooling or using a process called vitrification. Vitrification involves very rapid freezing. Both methods use a cryoprotectant solution to protect the embryos from any damage due to freezing.

How do frozen embryos stay alive?

When an embryo is cryopreserved, it is frozen to a temperature so low that all of the cellular processes (growth, aging, metabolism, etc.) are frozen too.

They're not 'alive' so much as they are frozen in time. Freezing embryos, or any cell, is like hitting the pause button.

Though embryo or egg freezing has only been done for about 25 years, cell cryopreservation has been done worldwide since the 1960s. 

The challenge here comes when water molecules in a cell transition into ice, which has the potential to damage elements of the cell if crystals form. To protect a cell from forming these ice crystals, scientists have developed rapid freezing solutions that minimize this crystal formation.

Why do frozen embryo transfers fail?

Sometimes an embryo will be transferred to the uterus but ultimately fail to implant or result in pregnancy. A failed transfer can happen for many reasons, but most fit in to one of two categories.

First, it is possible that the embryo was not at high enough quality to sustain a pregnancy and develop into a fetus. When this happens, it cannot be predicted. The embryo might look healthy and normal in the lab, but there's always a chance this might not be the case. 

The second category is when the uterus might not be ready for implantation. The health of the individual might not be optimal to sustain a pregnancy.

In all cases, your physician can provide advice to help give you better chances moving forward. For this reason, many people store multiple embryos, so they can try the process again once they are ready.

How long does a frozen embryo last?

There doesn't seem to be a limit on how long a frozen embryo remains viable. The largest study to date found no difference in clinical pregnancy rate, miscarriage, implantation, or live birth rate.

Typically, embryos are kept for an average of 10 years. The longest an embryo has been kept and transferred for was 30 years. It is important to keep in mind that the risks of pregnancy at an advanced age are higher, and many clinics will not transfer embryos to women over a certain age. 

Different countries and states/provinces have variable regulations on how long an embryo can be stored. Clinics may also have independent regulations for how long they are willing to store embryos. Lilia can help you be sure that the clinic you are working with allows for embryo storage timelines that align with your reproductive goals.

How do I use my frozen embryos?

To use your frozen embryos, you will need to again consult a fertility specialist. The frozen embryo transfer (FET) cycle involves the clinic thawing your frozen embryo and transferring it into a healthy uterus. The embryo transfer process has three major steps: pre-transfer, transfer, and post-transfer.


Before an embryo transfer can occur, the uterus must be ready to facilitate a pregnancy.

An embryo can be transferred during the natural menstrual cycle of someone who has a uterus, or a cycle can be stimulated medically. In the case of medical stimulation, doctors must first reduce your body's natural ovarian activity.

Either birth control pills or a hormone called leuprolide can shut off your natural ovarian function.

After about ten days of decreased ovarian activity, you will be given estradiol to help prepare your endometrium (uterine lining) to house the embryo upon transfer. The estradiol treatment lasts approximately two weeks.

During this time, the fertility team will monitor how your endometrial lining has developed and examine your estradiol levels.

Once your lining is thick enough, you will be given the hormone progesterone to take before the physical embryo transfer.

The hormones that you are given during this time are important to help you sustain and achieve pregnancy. Your doctor will go over with you the timing of these hormones.


The process of embryo transfer is very quick. One or two embryos are selected, thawed to body temperature for one day, and inserted into the uterus.

The first step in this implantation involves slightly opening the cervix and inserting a small catheter. The embryos are then transferred through this catheter into the uterus.

An ultrasound is used to guide the embryo transfer to the best spot in the uterus for implantation. You will likely also take a steroid medication for about a week to help aid in the implantation process.


After embryo transfer, you will visit the clinic again about two weeks later for an ultrasound to see if the transfer was successful and the embryo implanted within the uterus.

The hormones estradiol and progesterone are commonly continued until about ten weeks into your pregnancy to ensure that your body is taking over.

Most clinics will accept frozen embryos from any other clinic for transfer. There is no major stress if you move or need to complete the IVF process at another clinic. Lilia's experts can help you to be sure you are selecting clinics that allow this sort of mobility if it's something that you might need.

Alyssia egg freezer

Embryo freezing side effects

The process of embryo freezing is not without risk. While obtaining eggs for embryo freezing, there are inherent risks of ovarian stimulation, which a physician and fertility team closely monitor.

In terms of side-effects, many women experience light cramping and will take a few days following the embryo freezing procedure to recoup their energy.

Another consideration with from embryo transfer is the risk of multiple pregnancies, though this concern is less relevant today than it was 10 years ago.

Traditionally, when embryos were transferred physicians teams would often include more than one embryo to increase the odds of implantation. As a result, it was rather common for in-vitro fertilization to result in twins.

As IVF protocols have improved, it is less and less common for physicians to transfer multiple embryos. In fact, the American Society for Reproductive Medicine (ASRM) has guidelines on the number of embryos that should be transferred based on a patient's age and no longer recommends transferring multiple embryos for women under 38.

As such, these days most clinics will opt for single embryo transfer (SET) to avoid the risks of multiple pregnancies.

There are no reported side effects of using a frozen embryo on pregnancy complications when compared to using ‘fresh’ embryos.
ASMR Guidelines for Embryo Transfers

Common Reasons for Embryo Freezing

There are a number of reasons that a person or a couple may decide to undergo assisted reproductive technologies to preserve fertility or conceive their biological children after struggles with infertility.

Individuals may choose to freeze embryos if they are not quite ready to have children but would like to in the future and opt to forego freezing their eggs unfertilized.

Couples who do not produce sperm or who may struggle with infertility may also be interested in embryo freezing. It is quite common to freeze embryos after a fresh embryo transfer has been done.

Many embryos can be produced during one cycle of in vitro fertilization but do not necessarily need to be transferred to get pregnant. Any embryos left after a cycle can be saved if someone may want to become pregnant again in the future.

Which clinics are the best for embryo freezing? 

Much like with egg freezing, finding the perfect fertility clinic near you for embryo freezing is a time-intensive process.

To start, you'll want to find a clinic that has a positive and judgment-free environment.

On top of this, most women we advise consider the success rate of the clinic for embryo freezing and embryo transfer.

Finally, costs, timelines, and in-network insurance coverage all are likely to sway your decision.

Lilia was built to simplify your embryo (or egg) freezing process. We've done the research for you and let you put the entire experience on autopilot

Connect with us if you'd like a 10x more convenient embryo freezing process.
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