How freezing embryos plays a crucial role in IVF
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[April 19, 2024]
By Nancy Lapid
(Reuters) - The practice of freezing embryos as part of in vitro
fertilization (IVF) was thrown into chaos in Alabama this year, when the
state supreme court ruled that such embryos should be considered
children, exposing clinics to wrongful death claims in the event they
are destroyed in the thawing process.
In 2021, more than 80% of U.S. IVF procedures involved the transfer of
frozen embryos, according to a recent report by the U.S. Department of
Health and Human Services.
Undermining use of frozen embryos in IVF would introduce many
uncertainties, delays and possible additional expenses, according to
fertility experts. Here is what you need to know about the process and
its benefits:
HOW IS EMBRYO FREEZING USED IN IVF?
IVF uses high doses of hormones to stimulate ovaries to produce as many
eggs as possible. Once the eggs are extracted, the most mature are
selected for attempts at fertilization with sperm.
Over the next 5 to 6 days, healthy fertilized eggs grow into blastocysts
- the earliest stage of embryo - containing roughly 100-200 cells.
Blastocysts can be transferred into the uterus or frozen to be thawed
for later use.
After transfer into the uterus, if all goes well, the blastocyst
implants itself in the wall of the womb and continues to grow.
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Typically, if 20 eggs are retrieved after ovarian stimulation, about 16
will be mature, about 12 of those will fertilize when combined with
sperm, and perhaps six will grow into healthy blastocysts with good
potential for implanting and resulting in a successful pregnancy, said
Dr. Zev Williams, Chief of the division of reproductive endocrinology &
infertility at Columbia University Fertility Center in New York.
WHAT ARE SOME BENEFITS OF USING FROZEN EMBRYOS IN IVF?
For some patients, freezing embryos and then waiting several weeks
before a transfer into the uterus is more likely to lead to successful
implantation, depending on their age, underlying health or hormone
levels.
The pause allows the body's hormone levels to normalize following
ovarian stimulation. It also reduces the risk of ovarian
hyperstimulation syndrome (OHSS), a potentially life-threatening effect
of intense hormone use.
More broadly, freezing embryos often means that only one course of
painful, expensive ovarian stimulation and egg retrieval is needed. If
an embryo transfer fails, additional embryos can be thawed and used.
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![](../images/041924PIX/health8.jpg)
A medical technician selects eggs for an in-vitro fertilization (IVF)
procedure called Intracytoplasmic Sperm Injection (ICSI) at the
Laboratory of Reproductive Biology CECOS of Tenon Hospital in Paris,
France, September 19, 2019. Picture taken September 19, 2019.
REUTERS/Benoit Tessier/File Photo
![](http://archives.lincolndailynews.com/2024/Apr/19/images/ads/current/graue_lda_preowned_040824.jpg) Pregnancies with twins or triplets
were more common with IVF before embryo freezing, as doctors would
transfer more than one embryo at a time to increase the chances of a
successful pregnancy.
Freezing of embryos also allows patients to preserve fertility in
advance of chemotherapy or other treatments that can damage the
reproductive organs.
Genetic screening of embryos before a transfer is only possible with
freezing because it can take several weeks to get results. It is
often employed when there is a history of recurrent miscarriages,
previous IVF failures and maternal age over 35 or a family history
of genetic diseases.
WHAT IF FREEZING EMBRYOS FOR IVF BECAME UNAVAILABLE?
The loss of the option to freeze embryos for later usage "would
represent a significant setback for the field," said Dr. Steven
Spandorfer of Weill Cornell Medicine in New York City, president of
the American Society of Reproductive Medicine.
A single pregnancy is the best way to promote the birth of a healthy
child after IVF, so clinics are unlikely to return to the practice
of transferring multiple embryos into the womb, Spandorfer said.
Clinics could freeze eggs instead of embryos, but that approach has
many limitations that would lower the overall success of IVF.
The viability of those eggs would not be clear until they are
individually thawed and IVF is attempted, creating the potential for
delayed embryo transfers and the need for additional hormone use and
retrievals.
(Reporting by Nancy Lapid; Editing by Michele Gershberg and Bill
Berkrot)
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