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When in vitro fertilization (IVF) treatment first became available over 40 years ago, fresh embryo transfers were the only type of transfers available. This was because the science of freezing embryos (known as cryopreservation) wasn’t fully developed at that time.

Science has since then advanced and now the topic of fresh vs. frozen embryo transfer is a hot debate among the reproductive medicine community and fertility patients alike. Many argue that the success rate of frozen embryo transfer is higher — meaning potentially fewer IVF cycles (which includes egg retrieval and taking ovarian stimulation medications) needed for you to build your family. In this article, we’re going to go into the details of the two different modes of embryo transfer and talk about why freezing embryos has become the more favorable option in IVF practice.

Orchid offers advanced genetic testing for couples who want their child to have the best shot of a healthy life. As part of our “Pregnancy and Fertility” series, we distill down your fertility treatment options and help you navigate the complex process.

Fresh Vs. Frozen Embryo Transfer: What’s the Difference?

When it comes to the differences in the two modes of embryo transfer, there’s a bit more to it than a simple comparison that one is fresh and one is frozen. For example, the IVF timeline for a frozen embryo transfer looks different than that of a fresh embryo transfer.

Fresh Embryo Transfer

A fresh embryo is typically transferred back into the woman’s uterus five days after a patient’s eggs are retrieved. After retrieval, the eggs are fertilized with sperm in a lab, and the resulting embryos are grown and closely monitored until it’s time for implantation.

There are different protocols for the IVF process, some of them will include birth control pills and others don't. When birth control pills are used, the stimulation of the ovaries will start 5 days after the last pill. When birth control pills are not needed, the stimulation of the ovaries will start on day 2 of the menstrual period.

The goal of ovarian stimulation is to produce as many mature eggs as possible. After 9-13 days of stimulation when the size of the follicles is close to 18-22mm, the patient will inject the trigger shot(s) to complete the maturation of the eggs. 35 hours later, a reproductive endocrinologist will retrieve the eggs.

The primary benefit of fresh embryo transfers is that there’s a shorter conception window since there’s only a five-day waiting period between egg retrieval and embryo transfer into the uterus. Another benefit to fresh embryo transfers is that they’re sometimes more likely to be covered under a patient’s insurance policy, depending on which state they live in.

Frozen Embryo Transfer

A frozen embryo transfer is a much simpler procedure for patients and endocrinologists. Much like a fresh embryo transfer, the patient must go through IVF to collect as many mature eggs as possible. However, once the eggs are fertilized with sperm and embryos are created, they are then frozen via cryopreservation.

Typically, a frozen embryo transfer will occur between six and eight weeks after the embryo has been frozen.

There are two types of protocols for frozen embryo transfers.

1. Medicated frozen cycle — Estrogen supplementation is necessary to thicken the endometrial lining. Patients are monitored by ultrasound until the endometrial lining is ready. Progesterone supplementation is then added and the embryo transfer date is planned. A medicated cycle is the more common of the two options. ‍
2. Non-medicated frozen cycle — No hormonal medications are needed and patients are monitored by ultrasound until follicle size is close to 18-22 mm. Ovulation is then induced with a trigger shot to transfer the embryo at the right time. Progesterone supplementation may be indicated prior to embryo transfer.

Arguably the greatest benefit of a frozen embryo transfer is time and greater flexibility. Embryo freezing is a form of fertility preservation, allowing couples to choose when they would like to try getting pregnant without the added time pressure.

If more than one embryo is created, the remaining viable embryos can be frozen and later thawed for future use. Couples may choose to use these frozen embryos because a transferred embryo doesn’t result in pregnancy or more children are desired. Thus, there’s also the benefit of not having to undergo multiple rounds of IVF to grow your family.

Why Fertility Clinics are Beginning to Adopt Frozen Embryo Transfers

More and more fertility clinics are beginning to adopt frozen embryo transfers. Here are some reasons why:

• Fresh embryo transfers often require more stimulation medications with greater unpredictability. These medications may increase the levels of some hormones and may not be suitable for patients at risk of developing ovarian hyperstimulation syndrome. In addition, sometimes the endometrial lining may not be ready for embryo transfer, leading to canceled fresh embryo transfers. If the cycle is canceled, the patient will have a period and start again with a new cycle. 
• Frozen embryo transfer needs minimal or no medication and can be better planned. Since embryos are frozen, the transfer date can be planned and adjusted accordingly. If the endometrial lining is not yet ready, the clinical team can continue monitoring, increase the medication dosage, or reschedule the embryo transfer date to a later time if necessary. 
• Frozen embryo transfer may have better pregnancy success. Recent research suggests that frozen embryo transfers may lead to better pregnancy rates compared to fresh cycles. 
• Frozen embryo transfer gives patients the option to genetically test their embryos. Many patients now select the option of doing PGT-A (preimplantation genetic testing for aneuploidies). Embryos are sampled for genetic testing then frozen. This provides enough time for patients and their care time to receive genetic testing results and use the results to inform which embryo to transfer. Nowadays, if patients elect to do any form of genetic testing on their embryos through embryo sampling, patients almost always do frozen embryo transfers as opposed to fresh because the timing makes the most sense.

So, Fresh or Frozen?

While the research lends itself in favor of frozen embryo transfers, it doesn’t necessarily negate the benefits of fresh embryo transfers. For most, it would seem that frozen is the answer, although there are certain instances where a fresh transfer would be more beneficial to an individual.

Your fertility doctor will recommend whether you should consider fresh or frozen embryo transfer depending on factors such as age, predicted response to medications, number of quality of the embryos, previous cycle information, and medical history.

Fertility is a journey, and we’re here to help. Fertility treatment and reproductive medicine have come a long way since IVF was first introduced over 40 years ago. Today, advanced embryo testing is now available to couples who want their child to have the best shot of a healthy life. Explore how Orchid helps you conceive with confidence.