“Human Pregnancy Following Cryopreservation, Thawing and Transfer of an Eight-Cell Embryo” (1983), by Alan Trounson and Linda Mohr

In 1983, researchers Alan Trounson and Linda Mohr published the article “Human Pregnancy Following Cryopreservation, Thawing and Transfer of an Eight-Cell Embryo,” hereafter “Human Pregnancy,” in the journal Nature. In the article, the authors describe an experiment that led to one of the world’s first pregnancies through cryopreservation, or freezing, of an eight-cell human embryo. They discuss an experiment conducted at the Monash University and Queen Victoria Medical Center in Melbourne, Australia. Prior to the article’s publication, scientists had reported on embryonic cryopreservation experiments with animals only. At the end of the article, the authors mention that the pregnancy ended in a spontaneous miscarriage due to problems unrelated to cryopreservation twenty-four weeks after embryonic transfer. Despite the miscarriage, “Human Pregnancy” is one of the first articles to describe a successful human pregnancy after cryopreservation, and demonstrated that cryopreservation, as part of in vitro fertilization treatment, was a viable option for humans as well.

1. Background and Context
2. Article Roadmap
3. Detailed Content
4. Reception and Impact

Background and Context

The process of in vitro fertilization, or IVF, is a medical fertility procedure in which scientists fertilize an egg cell outside of a woman’s body. An egg cell is an unfertilized cell in the ovary, a female reproductive organ. Scientists take an egg cell from a woman’s body and fertilize it with sperm cells outside of the body so an embryo can develop. Physicians then take the embryo and place it inside the woman’s uterus. The uterus is an organ of the female reproductive system where an embryo begins the stages of early development into a fetus.

Cryopreservation is a technique used in IVF treatments that involves freezing and storing embryos for later use. An embryo can be frozen anytime from the two-to-eight cell stage up to the point it becomes a blastocyst, made up of hundreds of cells. Because a cell is mainly composed of water, when freezing an embryo, ice can form in a way that damages the cell. To prevent damage, physicians use fluids called cryoprotective agents, or CPAs, when freezing cells to slow the rate of ice crystal growth, water transportation into and out of the cell, and nucleation, or the beginning process of forming an ice crystal from a solution. Once the embryo is frozen, all biological activity stops, resulting in no further development of its cells. Physicians store the frozen embryo in a metal canister of liquid nitrogen at a sub-zero temperature. The addition of CPA allows for the embryo to be preserved as long as it remains in the cooled nitrogen container. An embryo can safely stay frozen for ten years or longer. After scientists thaw the embryo, it starts back up in the stage of development where it left off prior to being frozen.

Trounson and Mohr based the experiment they detail in “Human Pregnancy” on early animal studies in cryopreservation. In 1972, scientists conducted one of the first successful cryopreservation experiments on mice. One year later in 1973, an experiment led to one of the first births of a calf from cryopreservation. In 1983, the authors used those same procedures from mice and cow experiments in a human patient through thawing and transferring a cryopreserved human embryo, which led to a successful pregnancy.

At the time that Trounson and Mohr published “Human Pregnancy,” Trounson was working as a physician specializing in the study and treatment of embryos. He had been working as the Senior Research Fellow at Monash University in Melbourne, Australia, since 1977. Additionally, he was a contributing member of the Monash research team, a group of physicians responsible for many new advances in IVF techniques. Mohr, also a researcher from Monash University, specializes in cryopreservation and IVF as of 2024. Mohr and Trounson collaborated on six other publications focusing on IVF, cryopreservation, and pregnancy prior to “Human Pregnancy.”

Article Roadmap

“Human Pregnancy” consists of three untitled sections. In the first section of the paper, the authors discuss the total number of patients involved in the experiment, as well as their processes for freezing, thawing, ensuring the embryos developed correctly, and transferring the embryos to the patients’ uteri. In the second section of the paper, the authors mention that one patient became pregnant after transfer of a thawed embryo. The team notes that the patient miscarried eight weeks after transfer, but do not provide further details. The authors go on to state that four months later that patient tried a second IVF procedure using another cryopreserved embryo, which led to pregnancy, but a septic bacterial infection caused the patient’s pregnancy to end in a second spontaneous miscarriage after twenty-four weeks. In the last section, the authors go on to describe the benefits of cryopreservation, such as reduced cost from multiple IVF attempts. They also focus on ethical issues such as what would occur in case of death of one or both parents.

Detailed Content

In the first section of the paper, the authors describe how they procured fertilized embryos from the patients in the study. They cultured four- and eight-cell embryos outside of the patient’s body for thirty-four to sixty hours. The team then froze the embryos using either glycerol or DMSO, types of cryoprotectant. When it was time to transfer the embryo, the researchers thawed the embryos and removed the cryoprotectant. Doctors transferred the embryos to the patient’s uterus only if the embryos were at least fifty percent normal in shape and appearance four to twelve hours after thawing. Due to unspecified ethical restrictions on the work, Trounson and Mohr did not perform further assessments on the embryos. The authors specify that the team thawed sixteen embryos and transferred them to a total of fifteen patients. The authors mention that glycerol was difficult to remove after thawing, and that DMSO was the more successful cryoprotectant for slow and fast thawing.

In the second section of the paper, the authors state that only one out of the fifteen patients became pregnant from IVF, not only once but twice. However, both pregnancies resulted in a spontaneous miscarriage. The first embryo transfer was one of four embryos obtained from that patient. Four months after the first miscarriage, the couple requested a second round of IVF and doctors confirmed pregnancy. The pregnancy proceeded normally until week twenty-four when doctors could not detect fetal heartbeat due to severe inflammatory conditions and failure. The fetus was a stillborn female. The authors performed tests on the stillborn fetus and found that no abnormalities in the fetus were due to cryopreservation.

In the same section, the scientists detail some cell damage during the thawing process. Three blastomeres, or cells of the embryo, were damaged due to cryopreservation techniques. But because the pregnancy was able to continue despite that damage, the authors note that that finding suggests that not all blastomeres are required for a full-term pregnancy. They also write that there is little evidence linking initial cell damage to abnormalities in live newborn birth, which highlights the safety of using cryopreserved embryos for IVF.

In the third section, the authors discuss the potential benefits of embryo preservation, such as higher pregnancy rate and more time to perform genetic screening. Trounson and Mohr explain that freezing embryos can increase the pregnancy rates because scientists can create multiple frozen embryos from a single egg retrieval. Cryopreservation can also reduce costs and risks associated with multiple rounds of IVF treatments. Cryopreservation with IVF also provides individuals undergoing conditions that may result in a loss of fertility, such as chemotherapy, a chance to experience future pregnancy. The authors note that scientists can detect genetic abnormalities from cells from the frozen embryo. The team explains that some cells from a frozen embryo can be genetically screened and transferred to a patient’s uterus if no genetic complications arise. At the time of publication, the Australian National Health and Medicine Council limited embryo storage to ten years. However, the team notes that the embryo could technically be viable for longer.

At the end of the third section, the researchers shift to writing about ethical and legal debates for embryo storage. They question what the future of an embryo would be with the death of one or both parents, and suggest either donation of the embryo to another couple or disposal. During the time of publication, the Australian Law Reform Commission was discussing those issues. The authors finish by noting that at the time of publication, another pregnancy is twelve weeks underway using the same method of cryopreservation for a patient with blocked fallopian tubes.

Reception and Impact

The publication of “Human Pregnancy” in 1983 sparked ethical and legal debates among scientists and the general public, especially surrounding the question of what should happen to the embryos if the parents separated or if one or both of the parents died. In 1984, fifty-seven-year-old Mario Rios and forty-year-old Elsa Rios died in an unexpected plane crash when they had two embryos cryopreserved in a storage center in Melbourne, Australia. The plane crash instigated the question of storage limit, whether or not embryos have a right to legal status, and if they do, whether they should be subject to donation or disposal. After the plane crash, Victoria state law recommended a shortening of embryo storage limit from a maximum of ten years down to five years. The same committee also recommended that scientists destroy the embryos. However, the community opposed, and the Rios’s embryos were reportedly donated to another couple.

Since the article’s publication, cryopreservation has become an official procedure used in IVF centers worldwide. In 1985, one of the first IVF twins were born in Australia using cryopreserved embryos. Since then, cryopreservation has become commonplace. A study conducted in Europe by the European IVF Monitoring consortium from 2010 to 2014 counted over 34,000 cryopreservation cycles in seventeen countries. In the United States in 2014, scientists procured almost fifty percent of embryos for IVF procedures from cryopreservation cycles. As of 2024, scientists have majorly shifted to using a cryopreservation technique known as vitrification, that lowers the risk of ice formation when freezing embryos. Vitrification uses a higher concentration of CPAs and utilizes extremely rapid freezing techniques to avoid ice formation.

As of 2024, “Human Pregnancy” has been cited over 1,500 times and has been used as a guide for other procedures involving the thawing and transferring of cryopreserved embryos. Although the pregnancy in “Human Pregnancy” ended in a miscarriage, the article established cryopreservation as a safer, cheaper, and more efficient way for infertile couples to try to have families of their own. Since the publication of “Human Pregnancy,” scientists have developed new cryopreservation techniques and studied the best times to implant embryos that have led to an increase in pregnancy rates from frozen embryos, and a reduction in the cost and risk of undergoing multiple IVF treatments. Because of new developments in IVF, women with diseases that may lead to permanent infertility, such as endometriosis, or who receive chemotherapy, now have the option to preserve their fertility.