question: We can freeze human sperm and eggs indefinitely, without "killing" them. Why can't we do the same for whole people, or even just organs?
comment: Because sperm and eggs are just single cells. Organs and organisms are collections of cells that must operate in unison or the entire organism dies. If you have 5 million sperm cells and your freezing/thawing process kills half of them, you still have 2.5 million viable sperm cells to rely on, and only need one for success. If you freeze/thaw a person and kill half their cells, you end up with a mess.
passages: There are still warnings for women using this technology to fall pregnant at an older age as the risk of pregnancy complications increases with a mother's age. However, studies have shown that the risk of congenital abnormalities in babies born from frozen oocytes is not increased further when compared to naturally conceived babies.
  
  Section::::Risks.
   Cryopreservation in humans with regards to infertility involves preservation of embryos, sperm, or oocytes via freezing. Conception, "in vitro", is attempted when the sperm is thawed and introduced to the 'fresh' eggs, the frozen eggs are thawed and sperm is placed with the eggs and together they are placed back into the uterus or a frozen embryo is introduced to the uterus. Vitrification has flaws and is not as reliable or proven as freezing fertilized sperm, eggs, or embryos as traditional slow freezing methods because eggs alone are extremely sensitive to temperature. Many researchers are also freezing ovarian tissue in conjunction with the eggs in hopes that the ovarian tissue can be transplanted back into the uterus, stimulating normal ovulation cycles. In 2004, Donnez of Louvain in Belgium reported the first successful ovarian birth from frozen ovarian tissue. In 1997, samples of ovarian cortex were taken from a woman with Hodgkin's lymphoma and cryopreserved in a (Planer, UK) controlled-rate freezer and then stored in liquid nitrogen. Chemotherapy was initiated after the patient had premature ovarian failure. In 2003, after freeze-thawing, orthotopic autotransplantation of ovarian cortical tissue was done by laparoscopy and after five months, reimplantation signs indicated recovery of regular ovulatory cycles. Eleven months after reimplantation, a viable intrauterine pregnancy was confirmed, which resulted in the first such live birth – a girl named Tamara.
   There may also be some risks to any resulting child. These include IVF-associated risks such as multiple pregnancy, pregnancy-induced high blood pressure, premature delivery, operative delivery and infants displaying low birth weight. There also remain potential unknown risks caused by long-term freezing. Expanded use of Intracytoplasmic sperm injection (ICSI) to inject a single sperm into a thawed egg could additionally be a cause for concern as this method has been associated with a higher rate of birth defects.
  
  Section::::See also.
  
  BULLET::::- Egg donation
  
  BULLET::::- Semen cryopreservation
  
  BULLET::::- In vitro fertilization
  
  Section::::External links.
   BULLET::::- "Egg freezing." A woman can freeze her eggs preserve her fertility. By using egg freezing while in the peak reproductive years, a woman's oocytes are cryogenically frozen and ready for her use later in life, reducing her chances of female infertility.
  
  Section::::Treatment.
  
  There is no method to reverse advanced maternal age, but there are assisted reproductive technologies for many causes of infertility in pre-menopausal women, including:
  
  BULLET::::- Ovulation induction for anovulation
  
  BULLET::::- In vitro fertilization in for example tubal abnormalities
  
  Section::::Epidemiology.
   In 1949, bull semen was cryopreserved for the first time by a team of scientists led by Christopher Polge. This led to a much wider use of cryopreservation today, with many organs, tissues and cells routinely stored at low temperatures. Large organs such as hearts are usually stored and transported, for short times only, at cool but not freezing temperatures for transplantation. Cell suspensions (like blood and semen) and thin tissue sections can sometimes be stored almost indefinitely in liquid nitrogen temperature (cryopreservation). Human sperm, eggs, and embryos are routinely stored in fertility research and treatments. Controlled-rate and slow freezing are well established techniques pioneered in the early 1970s which enabled the first human embryo frozen birth (Zoe Leyland) in 1984. Since then, machines that freeze biological samples using programmable steps, or controlled rates, have been used all over the world for human, animal, and cell biology – 'freezing down' a sample to better preserve it for eventual thawing, before it is deep frozen, or cryopreserved, in liquid nitrogen. Such machines are used for freezing oocytes, skin, blood products, embryo, sperm, stem cells, and general tissue preservation in hospitals, veterinary practices, and research labs. The number of live births from 'slow frozen' embryos is some 300,000 to 400,000 or 20% of the estimated 3 million "in vitro" fertilized births. Dr Christopher Chen, Australia, reported the world’s first pregnancy using slow-frozen oocytes from a British controlled-rate freezer in 1986.
   "Controlled-rate and slow freezing", also known as "slow programmable freezing (SPF)", is a set of well established techniques developed during the early 1970s which enabled the first human embryo frozen birth Zoe Leyland during 1984. Since then, machines that freeze biological samples using programmable sequences, or controlled rates, have been used all over the world for human, animal and cell biology – "freezing down" a sample to better preserve it for eventual thawing, before it is frozen, or cryopreserved, in liquid nitrogen. Such machines are used for freezing oocytes, skin, blood products, embryo, sperm, stem cells and general tissue preservation in hospitals, veterinary practices and research laboratories around the world. As an example, the number of live births from frozen embryos 'slow frozen' is estimated at some 300,000 to 400,000 or 20% of the estimated 3 million in vitro fertilisation (IVF) births.
   Several independent studies have provided evidence that frozen embryos stored using slow-freezing techniques may in some ways be 'better' than fresh in IVF. The studies indicate that using frozen embryos and eggs rather than fresh embryos and eggs reduced the risk of stillbirth and premature delivery though the exact reasons are still being explored.
  
  Section::::Main methods to prevent risks.:Vitrification.
   Since 1999, when the birth of the first baby from an embryo derived from vitrified-warmed woman’s eggs was reported by Kuleshova and co-workers in the journal of Human Reproduction, this concept has been recognized and widespread. This break-through in achieving vitrification of woman’s oocytes made an important advance in our knowledge and practice of the IVF process, as clinical pregnancy rate is four times higher after oocyte vitrification than after slow freezing. Oocyte vitrification is vital for preservation fertility in young oncology patients and for individuals undergoing IVF who object, either for religious or ethical reasons, to the practice of freezing embryos.
   Recent modifications in protocol regarding cryoprotectant composition, temperature and storage methods have had a large impact on the technology, and while it is still considered an experimental procedure, it is quickly becoming an option for women. Slow freezing traditionally has been the most commonly used method to cryopreserve oocytes, and is the method that has resulted in the most babies born from frozen oocytes worldwide. Ultra-rapid freezing or vitrification represents a potential alternative freezing method.
   Supercooling was successfully applied to organ preservation at Massachusetts General Hospital/Harvard Medical School. Livers that were later transplanted into recipient animals were preserved by supercooling for up to 96 hours (4 days), quadrupling the limits of what could be achieved by conventional liver preservation methods. The livers were supercooled to a temperature of –6 °C in a specialized solution that protected against freezing and injury from the cold temperature.
   Slow cooling methods rely on the fact that cells contain few nucleating agents, but contain naturally occurring vitrifying substances that can prevent ice formation in cells that have been moderately dehydrated. Some cryobiologists are seeking mixtures of cryoprotectants for full vitrification (zero ice formation) in preservation of cells, tissues, and organs. Vitrification methods pose a challenge in the requirement to search for cryoprotectant mixtures that can minimize toxicity.
  
  Section::::Applied cryobiology.:In humans.
  
  Human gametes and two-, four- and eight-cell embryos can survive cryopreservation at -196 °C for 10 years under well-controlled laboratory conditions.
   The main techniques used for embryo cryopreservation are vitrification versus slow programmable freezing (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 than slow freezing.
   BULLET::::- Makler counter chamber (or disposable counting chamber)
  
  BULLET::::- Haemocytometer
  
  BULLET::::- Straw filling and sealing equipment
  
  BULLET::::- Freezing equipment (manual or programmable)
  
  BULLET::::- Carbon dioxide incubator (for embryos)
  
  BULLET::::- Laminar flow benches (for embryos)
  
  BULLET::::- Dry liquid nitrogen shipping tanks
  
  BULLET::::- Long-term liquid nitrogen storage tanks.
  
  Section::::Limitations.
   Embryos can be either “fresh” from fertilized egg cells of the same menstrual cycle, or “frozen”, that is they have been generated in a preceding cycle and undergone embryo cryopreservation, and are thawed just prior to the transfer, which is then termed "frozen embryo transfer" (FET). 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 (ICSI). In fact, pregnancy rates are increased following FET, and perinatal outcomes are less affected, compared to embryo transfer in the same cycle as ovarian hyperstimulation was performed. The endometrium 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 than those born from non-frozen blastocysts. When transferring a frozen-thawed oocyte, the chance of pregnancy is essentially the same whether it is transferred in a natural cycle or one with ovulation induction.
   Cryopreservation itself has always played a central role in assisted reproductive technology. With the first cryopreservation of sperm in 1953 and of embryos twenty five years later, these techniques have become routine. Dr Christopher Chen of Singapore reported the world's first pregnancy in 1986 using previously frozen oocytes. This report stood alone for several years followed by studies reporting success rates using frozen eggs to be much lower than those of traditional in vitro fertilization (IVF) techniques using fresh oocytes. Providing the lead to a new direction in cryobiology, Dr. Lilia Kuleshova was the first scientist to achieve vitrification of human oocytes that resulted in a live birth in 1999. Then recently, two articles published in the journal, "Fertility and Sterility", reported pregnancy rates using frozen oocytes that were comparable to those of cryopreserved embryos and even fresh embryos. These newer reports affirm that oocyte cryopreservation technology is advancing.
   Cryopreservation was applied to humans beginning in 1954 with three pregnancies resulting from the insemination of previously frozen sperm. Fowl sperm was cryopreserved in 1957 by a team of scientists in the UK directed by Christopher Polge. During 1963, Peter Mazur, at Oak Ridge National Laboratory in the U.S., demonstrated that lethal intracellular freezing could be avoided if cooling was slow enough to permit sufficient water to leave the cell during progressive freezing of the extracellular fluid. That rate differs between cells of differing size and water permeability: a typical cooling rate around 1 °C/minute is appropriate for many mammalian cells after treatment with cryoprotectants such as glycerol or dimethyl sulphoxide, but the rate is not a universal optimum.
   BULLET::::- Intracellular ice formation: While some organisms and tissues can tolerate some extracellular ice, any appreciable intracellular ice is almost always fatal to cells.
  
  Section::::Main methods to prevent risks.
  
  The main techniques to prevent cryopreservation damages are a well established combination of "controlled rate and slow freezing" and a newer flash-freezing process known as "vitrification".
  
  Section::::Main methods to prevent risks.:Slow programmable freezing.
   Section::::Freezable tissues.
  
  Generally, cryopreservation is easier for thin samples and small clumps of individual cells, because these can be cooled more quickly and so require lesser doses of toxic cryoprotectants. Therefore, cryopreservation of human livers and hearts for storage and transplant is still impractical.
  
  Nevertheless, suitable combinations of cryoprotectants and regimes of cooling and rinsing during warming often allow the successful cryopreservation of biological materials, particularly cell suspensions or thin tissue samples. Examples include:
  
  BULLET::::- Semen in semen cryopreservation
  
  BULLET::::- Blood
  
  BULLET::::- Special cells for transfusion
   The production of PF24 began in response to an increase in reported cases of transfusion-related acute lung injury, or TRALI. The proposed mechanism of TRALI involves antibodies from donor blood components (predominantly plasma) that are directed against human leukocyte antigens (HLA). These antibodies are most numerous in women who have been pregnant more than once. Thus, removing these women from the donor pool for frozen plasma was proposed as a solution to the TRALI problem (the women’s plasma could still be used for production of other components, including cryoprecipitate). However, removing roughly half of the donor pool was not a viable alternative, given the increasing need for plasma transfusion.
   Section::::Indications.
  
  Oocyte cryopreservation can increase the chance of a future pregnancy for three key groups of women: 
  
  BULLET::::1. those diagnosed with cancer who have not yet begun chemotherapy or radiotherapy;
  
  BULLET::::2. those undergoing treatment with assisted reproductive technologies who do not consider embryo freezing an option; and
  
  BULLET::::3. those who would like to preserve their future ability to have children, either because they do not yet have a partner, or for other personal or medical reasons.
   Frozen pelvis is sometimes classified into one of several patterns:
  
  BULLET::::- Centrifugal
  
  BULLET::::- Centripetal
  
  BULLET::::- Left-frozen
  
  BULLET::::- Complete
  
  Section::::Outcomes.
  
  If undiagnosed and untreated, complications can include bowel obstruction, several kinds of hydronephrosis and other damage to the urinary tract, and damage to pelvic nerves. 
   Oocyte cryopreservation is an option for individuals undergoing IVF who object, either for religious or ethical reasons, to the practice of freezing embryos. Having the option to fertilize only as many eggs as will be utilized in the IVF process, and then freeze any remaining unfertilized eggs can be a solution. In this way, there are no excess embryos created, and there need be no disposition of unused frozen embryos, a practice which can create complex choices for certain individuals.
   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.
  
  Section::::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.
  
  Section::::History.
   Without cryoprotectants, cell shrinkage and high salt concentrations during freezing usually prevent frozen cells from functioning again after thawing. Ice crystals can also disrupt connections between cells that are necessary for organs to function. The difficulties of recovering large animals and their individual organs from a frozen state have been long known. Attempts to recover frozen mammals by simply rewarming them were abandoned by 1957. At present, only cells, tissues, and some small organs can be reversibly cryopreserved.
   Embryo transfer is also used in laboratory mice. For example, embryos of genetically modified strains that are difficult to breed or expensive to maintain may be stored frozen, and only thawed and implanted into a pseudopregnant dam when needed.
  
  Section::::Embryo transfer in animals.:Frozen embryo transfer in animals.
  
presuppositions: If sperm and eggs can be frozen without reprocussions then there is no reason that humans can't be as well.  Human sperm and egg cells are not killed when frozen, therefore whole people and organs will also not be killed when frozen.
corrections: Sperm and eggs are only cells, and the quantity is in the millions. Freezing sperm and/or eggs can kill some but they usually survive, if a person is frozen and multiple cells die within the person, it causes organ dysfunction, which could be very harmful or fatal to the human.  Freezing does kill sperm and egg cells the same way freezing kills cells of whole organisms or organs, however organs and organisms are collections of cells working in unison where as sperm and eggs are viable with one cell. 
raw_presuppositions: If sperm and eggs can be frozen without reprocussions then there is no reason that humans can't be as well.  Human sperm and egg cells are not killed when frozen, therefore whole people and organs will also not be killed when frozen. Freezing sperm does not kill them.
raw_corrections: Sperm and eggs are only cells, and the quantity is in the millions. Freezing sperm and/or eggs can kill some but they usually survive, if a person is frozen and multiple cells die within the person, it causes organ dysfunction, which could be very harmful or fatal to the human.  Freezing does kill sperm and egg cells the same way freezing kills cells of whole organisms or organs, however organs and organisms are collections of cells working in unison where as sperm and eggs are viable with one cell.  Freezing sperm can kill some of the sperm, but there are still plenty left.