Confused about the difference between frozen embryos and egg freezing? Experts break it down.

The Alabama Supreme Court ruled on Feb. 16 that frozen embryos can be considered “children” under state law, which was swiftly followed by multiple fertility centers, including the University of Alabama at Birmingham hospital and Alabama Fertility, putting in vitro fertilization (IVF) treatments temporarily on hold while they sort through the possible legal repercussions.

The ruling has stunned doctors and left fertility patients worried about how this will impact them. It’s also led to a lot of confusion and questions about IVF treatments, particularly about frozen embryos and egg freezing. To help clear up the confusion in the aftermath of the ruling, Yahoo Life reached out to fertility experts to explain what some of these common terms in reproductive medicine mean. Here’s what you need to know.

What is a frozen embryo?

Embryos are eggs that have been fertilized with sperm. “They can be frozen for future use, at which time the embryo is thawed and transferred into the woman’s uterus,” Dr. Daniel Stein, medical director of WIN, which provides fertility services, tells Yahoo Life.

What is the difference between freezing embryos and freezing eggs?

The main difference is that egg freezing involves eggs that are unfertilized, while embryo freezing involves eggs that have been fertilized with sperm, aka embryos. (It’s worth noting that sperm can also be frozen.) Egg freezing is more common than freezing embryos, which require a partner or sperm donor for fertilization.

“Freezing eggs and freezing embryos require the same process; the only difference is whether or not that egg has already been fertilized,” Dr. Aimee Eyvazzadeh, fertility specialist and medical advisor for Proov, which provides at-home fertility tests, tells Yahoo Life. “An egg is a chance for an embryo, which is a chance for a baby. The number of eggs it takes to get from egg to embryo to baby depends on several factors, such as the woman's age, egg quality and genetics. For example, for a 20-year-old female, it may only take one egg to turn into a healthy baby. For a 40-year-old, it could take 50 eggs to have one healthy embryo that will turn into a baby.”

Why do people typically freeze eggs or embryos?

There are several reasons. “People typically freeze eggs as a way to preserve their fertility,” Dr. Asima Ahmad, co-founder and chief medical officer of Carrot Fertility, tells Yahoo Life. “Though embryos can also be frozen for fertility preservation, there are several other reasons someone may choose to freeze embryos.”

Embryo freezing allows patients going through fertility treatments, for example, to store embryos for possible later use. “They may want the option of growing their family in the future and may choose to freeze embryos to use them at a later point in time to have children,” explains Ahmad. “Sometimes this is done for medical reasons, such as a diagnosis of cancer, so that when the treatment is complete and they are ready to build their family, they can use the embryo.”

Eyvazzadeh explains that, as part of the IVF process, it’s common practice to create more embryos than you plan to transfer. Patients going through IVF may freeze those excess embryos. Ahmad says this is important since, for most people, “a single embryo being transferred to the uterus is the safest option — the goal is for a singleton pregnancy, as that is the safest thing for the pregnant person and the baby,” she says. “Transferring multiple embryos to the uterus increases the likelihood of a multiple gestation pregnancy — such as twins, triplets — and results in a higher-risk pregnancy that could result in complications for the pregnant person and babies.”

Egg freezing, on the other hand, is “solely for the purpose of fertility preservation, which can be done for a number of reasons,” says Stein. “Some women freeze eggs because they do not currently have a partner or do not wish to become pregnant today but are concerned about the loss of eggs that occurs as the woman ages. Other women freeze eggs before undergoing ovarian surgery, chemotherapy or radiation therapy, as such treatments might significantly reduce the woman’s egg supply.”

How long is a frozen embryo viable for? Where are they typically stored?

Frozen embryos can be stored in liquid nitrogen tanks within the facility they were produced in or at outside facilities that specialize in cryopreservation, says Stein — and they have a long shelf life.

“Frozen embryos have been successfully thawed — with successful pregnancies — after several years of freezing,” he says. While frozen embryos can be safely stored for 10 years or more, according to Johns Hopkins Medicine, Ahmad notes that, “Technically, if embryos are frozen and stored properly, there is no expiration date on how long they can remain frozen.”

That said, “It is not known whether there is a time frame above which embryos will not routinely thaw well,” says Stein. And as Ahmad points out, “In some cases, there may be certain practices or laws that say that the eggs can only be stored for a certain time and need to be used by then.”

Under what circumstances do patients discard frozen embryos?

It’s common in the IVF process to discard frozen embryos if they have genetic abnormalities or are no longer needed by the patient. “Couples who have completed childbearing might wish to discard any remaining embryos they have frozen,” says Stein. “Couples may also decide to discard embryos that have been deemed genetically abnormal by PGT testing,” or preimplantation genetic testing, which screens cells from embryos during the IVF process, including making sure embryos have the correct number of chromosomes before they are implanted in the patient. In some cases, abnormalities can mean “the embryo would likely not result in pregnancy, result in miscarriage or have a severe medical condition not compatible with life,” says Ahmad, so it may be discarded.

Under Alabama’s Wrongful Death Act, however, medical providers may be held legally responsible for discarding these embryos, or patients may find themselves having to cover the cost of storing their frozen embryos in perpetuity.

“The dust has not settled yet in Alabama regarding the effects of the ruling,” says Stein. “Couples are rightfully concerned that if embryos cannot be destroyed, the couples might be forced to use those embryos, leading to larger families than they had hoped for, or the couples would be forced to continue paying for storage indefinitely. Physicians and embryologists are concerned that any loss of embryos that occurs during the manipulation and transport of the embryos could lead to a wrongful death charge.”

The biggest impact right now, says Stein, is that “care for many in Alabama has been suspended due to clinics pausing care while the situation develops and until they can understand the ramifications.”