Embryo cryopreservation

Cryopreservation of embryos is the process of

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[5]^[6]

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.^[7]

Pregnancy outcome and determinants

In current

Oocyte age, survival proportion, and number of transferred embryos are predictors of pregnancy outcome.[12]

Pregnancies have been reported from embryos stored for 27 years.^[13] 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.^[12] 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.^[12]

A study in France between 1999 and 2011 came to the result that embryo freezing before administration of gonadotoxic chemotherapy 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.^[14]

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.^[15]

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.^[16] 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.^[16] 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.^[17] The first twins derived from frozen embryos were born in February 1985.^[18] 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, India 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^[19] 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.^[20][21]

Implications

The practice of cryopreservation of embryos has increased in recent years.^[22] 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.^[22] 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.^[22] Cryopreservation enables the embryos to be safely stored for extensive periods of time.^[16] 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.^[16] Doing so reduces the possibility of conceiving twins or triplets, thus allowing parents to exercise greater control over their vision for their families.^[16] Additionally, embryos may be tested and manipulated to eliminate genetic diseases.^[23]

Legal implications

While the cryopreservation of embryos has been characterized by great scientific developments over the years,^[23] 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.^[23] 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.^[24] 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.^[24] 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.^[25]

References