In 2021, over 80% of U.S. in vitro fertilization procedures involved the transfer of frozen embryos, according to a report by the U.S. Department of Health and Human Services.

The potential reduction in the use of frozen embryos in in vitro fertilization (IVF) could introduce uncertainties, delays, and possible additional expenses, according to fertility specialists. Here is an overview of the process and its benefits:

Embryo Freezing in IVF

IVF involves using high doses of hormones to stimulate the ovaries to produce multiple eggs. Once retrieved, the most mature eggs are selected for fertilization with sperm.

Over the next five to six days, fertilized eggs develop into blastocysts, containing approximately 100-200 cells. These blastocysts can be transferred into the uterus immediately or frozen for future use.

After uterine transfer, successful implantation of the blastocyst in the uterine wall leads to pregnancy.

Typically, from 20 retrieved eggs, approximately 16 are mature, 12 may fertilize, and about six develop into viable blastocysts with good implantation potential, according to Zev Williams, MD, Chief of the Division of Reproductive Endocrinology and Infertility at Columbia University Fertility Center.

Benefits of Using Frozen Embryos in IVF

For some patients, delaying embryo transfer after freezing can improve implantation success, depending on age, health, or hormone levels. This pause allows normalization of hormone levels post-stimulation and reduces the risk of ovarian hyperstimulation syndrome, a severe effect of intense hormone use.

Additionally, freezing embryos can limit the need for multiple painful and costly ovarian stimulation and egg retrieval procedures. If an embryo transfer fails, previously frozen embryos can be used.

The practice of transferring multiple embryos, which increased the likelihood of multiple pregnancies, has decreased due to the availability of frozen embryos.

Freezing embryos also permits fertility preservation before chemotherapy or other treatments that may impair reproductive function.

Preimplantation genetic testing is facilitated by embryo freezing, as the results take several weeks. This screening is often utilized in cases of recurrent miscarriages, previous IVF failures, maternal age over 35, or a family history of genetic disorders.

Implications of Unavailability of Embryo Freezing in IVF

The unavailability of embryo freezing would significantly impact the field, according to Steven Spandorfer, MD of Weill Cornell Medicine, President of the Society for Assisted Reproductive Technology. Single embryo transfer is preferred to ensure healthy singleton pregnancies, and clinics are unlikely to revert to transferring multiple embryos.

While egg freezing is an alternative, it has limitations that may reduce IVF success rates. The viability of frozen eggs is uncertain until thawed and fertilized, potentially delaying embryo transfers and necessitating additional hormone treatments and egg retrievals.