Cryopreservation of embryos is the process of
preserving an
embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
at sub-zero temperatures, generally at an
embryogenesis
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
stage corresponding to pre-implantation, that is, from
fertilisation
Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
to the
blastocyst
The blastocyst is a structure formed in the early embryonic development of mammals. It possesses an inner cell mass (ICM) also known as the ''embryoblast'' which subsequently forms the embryo, and an outer layer of trophoblast cells called the t ...
stage.
Indications
Embryo cryopreservation is useful for leftover embryos after a cycle of
in vitro fertilisation
In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating an individual's ovulatory process, removing an ovum or ova (egg or eggs) ...
, as patients who fail to conceive may become pregnant using such embryos without having to go through a full IVF cycle. Or, if pregnancy occurred, they could return later for another pregnancy. Spare oocytes or embryos resulting from fertility treatments may be used for
oocyte donation
Egg donation is the process by which a woman donates eggs to enable another woman to conceive as part of an assisted reproduction treatment or for biomedical research. For assisted reproduction purposes, egg donation typically involves in vitro fe ...
or
embryo donation Embryo donation is one disposition option for users of in vitro fertilisation with remaining fresh or frozen embryos. It is defined as the giving—generally without compensation—of embryos remaining after in vitro fertilization procedures to rec ...
to another woman or couple, and embryos may be created, frozen and stored specifically for transfer and donation by using donor eggs and sperm.
Method
Embryo cryopreservation is generally performed as a component of
in vitro fertilization
In vitro fertilisation (IVF) is a process of fertilisation where an egg is combined with sperm in vitro ("in glass"). The process involves monitoring and stimulating an individual's ovulatory process, removing an ovum or ova (egg or eggs) ...
(which generally also includes
ovarian hyperstimulation,
egg retrieval Transvaginal oocyte retrieval (TVOR), also referred to as oocyte retrieval (OCR), is a technique used in in vitro fertilization (IVF) in order to remove oocytes from the ovary of a woman, enabling fertilization outside the body. Transvaginal oocyt ...
and
embryo transfer
Embryo transfer refers to a step in the process of assisted reproduction in which embryos are placed into the uterus of a female with the intent to establish a pregnancy. This technique (which is often used in connection with in vitro fertilizati ...
). The ovarian hyperstimulation is preferably done by using a
GnRH agonist
A gonadotropin-releasing hormone agonist (GnRH agonist) is a type of medication which affects gonadotropins and sex hormones. They are used for a variety of indications including in fertility medicine and to lower sex hormone levels in the treatm ...
rather than
human chorionic gonadotrophin (hCG) for
final oocyte maturation, since it decreases the risk of
ovarian hyperstimulation syndrome
Ovarian hyperstimulation syndrome (OHSS) is a medical condition that can occur in some women who take fertility medication to stimulate egg growth, and in other women in very rare cases. Most cases are mild, but rarely the condition is severe and c ...
with no evidence of a difference in
live birth rate Pregnancy rate is the success rate for getting pregnant. It is the percentage of all attempts that leads to pregnancy, with attempts generally referring to menstrual cycles where insemination or any artificial equivalent is used, which may be simple ...
(in contrast to fresh cycles where usage of GnRH agonist has a lower live birth rate).
The main techniques used for embryo cryopreservation are
vitrification
Vitrification (from Latin ''vitreum'', "glass" via French ''vitrifier'') is the full or partial transformation of a substance into a glass, that is to say, a non-crystalline amorphous solid. Glasses differ from liquids structurally and glasses po ...
versus
slow programmable freezing
Cryo-preservation or cryo-conservation is a process where organisms, organelles, cells, tissues, extracellular matrix, organs, or any other biological constructs susceptible to damage caused by unregulated chemical kinetics are preserved by c ...
(SPF). Studies indicate that vitrification is superior or equal to SPF in terms of survival and implantation rates.
[ Vitrification appears to result in decreased risk of ]DNA damage
DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA da ...
than slow freezing. Vitrification prevent ice crystals in gametes. It is so fast (-23000 °C/min) that these crystals do not appear. Still, the amount of cryoprotectant used in the vitrification is crucial: too much is toxic for the embryo; but too little could cause the appearance of crystallised water, regardless of the speed at which the process is carried out.
Direct Frozen Embryo Transfer: Embryos can be frozen by SPF in ethylene glycol freeze media and transfer directly to recipients immediately after water thawing without laboratory thawing process. The world's first crossbred bovine embryo transfer calf under tropical conditions was produced by such technique on 23 June 1996 by Dr. Binoy S Vettical of Kerala Livestock Development Board, Mattupatti
Prevalence
World usage data is hard to come by but it was reported in a study of 23 countries that almost 42,000 frozen human embryo transfers were performed during 2001 in Europe.
Pregnancy outcome and determinants
In current state of the art
The state of the art (sometimes cutting edge or leading edge) refers to the highest level of general development, as of a device, technique, or scientific field achieved at a particular time. However, in some contexts it can also refer to a level ...
, early embryos having undergone cryopreservation implant at the same rate as equivalent fresh counterparts. The outcome from using cryopreserved embryos has uniformly been positive with no increase in birth defects or development abnormalities, also between fresh versus frozen eggs used for intracytoplasmic sperm injection
Intracytoplasmic sperm injection (ICSI ) is an in vitro fertilization (IVF) procedure in which a single sperm cell is injected directly into the cytoplasm of an egg. This technique is used in order to prepare the gametes for the obtention of emb ...
(ICSI). In fact, pregnancy rate Pregnancy rate is the success rate for getting pregnant. It is the percentage of all attempts that leads to pregnancy, with attempts generally referring to menstrual cycles where insemination or any artificial equivalent is used, which may be simple ...
s are increased following frozen embryo transfer
Embryo transfer refers to a step in the process of assisted reproduction in which embryos are placed into the uterus of a female with the intent to establish a pregnancy. This technique (which is often used in connection with in vitro fertilizatio ...
, and perinatal outcomes are less affected, compared to embryo transfer in the same cycle as ovarian hyperstimulation was performed. The endometrium
The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The functional laye ...
is believed to not be optimally prepared for implantation following ovarian hyperstimulation, and therefore frozen embryo transfer avails for a separate cycle to focus on optimizing the chances of successful implantation. Children born from vitrified blastocysts have significantly higher birthweight
Birth weight is the body weight of a baby at its birth. The average birth weight in babies of European descent is , with the normative range between . On average, babies of South Asian and Chinese descent weigh about . As far as low birth weight ...
than those born from non-frozen blastocysts. For early cleavage embryos, frozen ones appear to have at least as good obstetric outcome, measured as preterm birth and low birthweight for children born after cryopreservation as compared with children born after fresh cycles.[
Oocyte age, survival proportion, and number of transferred embryos are predictors of pregnancy outcome.][
Pregnancies have been reported from embryos stored for 27 years. A study of more than 11,000 cryopreserved human embryos showed no significant effect of storage time on post-thaw survival for IVF or oocyte donation cycles, or for embryos frozen at the pronuclear or cleavage stages.] In addition, the duration of storage had no significant effect on clinical pregnancy, miscarriage, implantation, or live birth rate, whether from IVF or oocyte donation cycles.[
A study in France between 1999 and 2011 came to the result that embryo freezing before administration of gonadotoxic ]chemotherapy
Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...
agents to females caused a delay of treatment in 34% of cases, and a live birth in 27% of surviving cases who wanted to become pregnant, with the follow-up time varying between 1 and 13 years.
Legislation
From 1 October 2009, human embryos are allowed to be stored for 10 years in the UK, according to the Human Fertilisation and Embryology Act 2008
The Human Fertilisation and Embryology Act 2008 (c 22) is an Act of the Parliament of the United Kingdom. The Act constitutes a major review and update of the Human Fertilisation and Embryology Act 1990.
According to the Department of Health the ...
.
History
The cryopreservation of embryos was first successfully attempted in 1984 in the case of Zoe Leyland, the first baby to be born from a frozen embryo. In Zoe's case, the embryo had been frozen for two months, but since the inception of the practice of cryopreservation after successful IVF, embryos have successfully survived in cryopreservation extensively longer periods of time, spanning even decades. The long-term implications of freezing embryos are demonstrated in the case of Molly Everette Gibson, the child born from the viable pregnancy of her mother who used an embryo, which had been stored in a cryogenic freezer for twenty-seven years. The first twins derived from frozen embryos were born in February 1985. Since then and up to 2008 it is estimated that between 350,000 and half a million IVF babies have been born from embryos frozen at a controlled rate and then stored in liquid nitrogen; additionally a few hundred births have been born from vitrified oocytes but firm figures are hard to come by.
It may be noted that Subash Mukhopadyay from Kolkata
Kolkata (, or , ; also known as Calcutta , the official name until 2001) is the capital of the Indian state of West Bengal, on the eastern bank of the Hooghly River west of the border with Bangladesh. It is the primary business, comme ...
, India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
reported the successful cryopreservation of an eight cell embryo, storing it for 53 days, thawing and replacing it into the mother's womb, resulting in a successful and live birth as early as 1978- a full five years before Trounson and Mohr had done so. A small publication of Mukherjee in 1978 clearly shows that Mukherjee was on the right line of thinking much before anyone else had demonstrated the successful outcome of a pregnancy following the transfer of a 8-cell frozen-thawed embryo into human subjects transferring 8-cell cryopreserved embryos.
Implications
The practice of cryopreservation of embryos has increased in recent years. While the original purpose of freezing embryos was to help heterosexual couples who struggled with infertility, the practice has become an increasingly common avenue to start a family for homosexual couples, single women, as well as surrogates. Prior to successful attempts to effectively freeze embryos for later use, individuals were limited in their assisted reproductive technology options to in vitro fertilization (IVF), whereby sperm and egg were combined in a lab to create the embryos, all of which then had to be immediately implanted into the mother. Cryopreservation enables the embryos to be safely stored for extensive periods of time. Individuals are then able choose the proper time to use the embryos as well as elect to use only one embryo at a time while saving the others for later use. Doing so reduces the possibility of conceiving twins or triplets, thus allowing parents to exercise greater control over their vision for their families. Additionally, embryos may be tested and manipulated to eliminate genetic diseases.
Legal Implications
While the cryopreservation of embryos has been characterized by great scientific developments over the years, the treatment of allocation of embryos in the event of a divorce or separation of the parties is a broadening and still less developed area of the law which continues to present challenges for the courts today. Politicians, state legislatures, and courts grapple with a multitude of legal issues surrounding families created using fertility treatments in view of divergent moral, political, and legal discourse throughout the United States. For example, in Illinois, the courts employ at least two clear approaches to determining how embryos are allocated in the event of a divorce or separation of the parties.
/ref> Specifically, the courts seek to enforce any contractual language surrounding the allocation of the embryos, and they also employ a balancing test of the parties’ interests alongside the contractual approach or simply as an alternative approach if no contract exists. State courts are often left to decide these issues as statutory resources are not well-developed across the states. For example, in Illinois, the Illinois Parentage Act of 2015 has contemplated situations in which parties, represented by independent legal counsel, enter into contractual agreements regarding the allocation of embryos, but no uniform statutory answer exists for situations in which parties failed to enter into such written agreements regarding allocation.
References
{{Assisted reproductive technology
Assisted reproductive technology
Cryopreservation