a monosomy for the chromosome on which the markers are located, or, possibly, as haploid. the appearance of a single allele that indicates an affected genotype is considered sufficient to diagnose the embryo as affected, and embryos that have been diagnosed with a complete unaffected genotype are preferred for replacement. although this policy may lead to a lower number of unaffected embryos suitable for transfer, it is considered preferable to the possibility of a misdiagnosis. preimplantation genetic haplotyping main article: preimplantation genetic haplotyping preimplantation genetic haplotyping (pgh) is a pgd technique wherein a haplotype of genetic markers that have statistical associations to a target disease are identified rather than the mutation causing the disease. once a panel of associated genetic markers have been established for a particular disease it can be used for all carriers of that disease. in contrast, since even a monogenic disease can be caused by many different mutations within the affected gene, conventional pgd methods based on finding a specific mutation would require mutation-specific tests. thus, pgh widens the availability of pgd to cases where mutation-specific tests are unavailable. pgh also has an advantage over fish in that fish is not usually able to make the differentiation between embryos that possess the balanced form of a chromosomal translocation and those carrying the homologous normal chromosomes. this inability can be seriously harmful to the diagnosis made. pgh can make the distinction that fish often cannot. pgh does this by using polymorphic markers that are better suited at recognizing translocations. these polymorphic markers are able to distinguish between embryos that carried normal, balanced, and unbalanced translocations. fish also requires more cell fixation for analysis whereas pgh requires only transfer of cells into polymerase chain reaction tubes. the cell transfer is a simpler method and leaves less room for analysis failure. embryo transfer and cryopreservation of surplus embryos embryo transfer is usually performed on day three or day five post-fertilization, the timing depending on the techniques used for pgd and the standard procedures of the ivf centre where it is performed. with the introduction in europe of the single-embryo transfer policy, which aims at the reduction of the incidence of multiple pregnancies after art, usually one embryo or early blastocyst is replaced in the uterus. serum hcg is determined at day 12. if a pregnancy is established, an ultrasound examination at 7 weeks is performed to confirm the presence of a fetal heartbeat. couples are generally advised to undergo pnd because of the, albeit low, risk of misdiagnosis. it is not unusual that after the pgd, there are more embryos suitable for transferring back to the woman than necessary. for the couples undergoing pgd, those embryos are very valuable, as the couple's current cycle may not lead to an ongoing pregnancy. embryo cryopreservation and later thawing and replacement can give them a second chance to pregnancy without having to redo the cumbersome and expensive art and pgd procedures. side effects to embryo pgd/pgs is an invasive procedure that requires a serious consideration, according to michael tucker, ph.d., scientific director and chief embryologist at georgia reproductive specialists in atlanta. one of the risks of pgd includes damage to the embryo during the biopsy procedure (which in turn destroys the embryo as a whole), according to serena h. chen, m.d., a new jersey reproductive endocrinologist with irms reproductive medicine at saint barnabas. another risk is cryopreservation where the embryo is stored in a frozen state and thawed later for the procedure. about 20% of the thawed embryos do not survive. there has been a study indicating a biopsied embryo has a less rate of surviving cryopreservation. another study suggests that pgs with cleavage-stage biopsy results in a significantly lower live birth rate for women of advanced maternal age. also, another study recommends the caution and a long term follow-up as pgd/pgs increases the perinatal death rate in multiple pregnancies. in a mouse model study, pgd has been attributed to various long term risks including a weight gain and memory decline; a proteomic analysis of adult mouse brains showed significant differences between the biopsied and the control groups, of which many are closely associated with neurodegenerative disorders like alzheimer's and down syndrome. ethical issues pgd has raised ethical issues, although this approach could reduce reliance on fetal deselection during pregnancy. the technique can be used for prenatal sex discernment of the embryo, and thus potentially can be used to select embryos of one sex in preference of the other in the context of "family balancing". it may be possible to make other "social selection" choices in the future that introduce socio-economic concerns. only unaffected embryos are implanted in a woman's uterus; those that are affected are either discarded or donated to science. pgd has the potential to screen for genetic issues unrelated to medical necessity, such as intelligence and beauty, and against negative traits such as disabilities. the medical community has regarded this as a counterintuitive and controversial suggestion. the prospect of a "designer baby" is closely related to the pgd technique, creating a fear that increasing frequency of genetic screening will move toward a modern eugenics movement. on the other hand, a principle of procreative beneficence is proposed, which is a putative moral obligation of parents in a position to select their children to favor those expected to have the best life. an argument in favor of this principle is that traits (such as empathy, memory, etc.) are "all-purpose means" in the sense of being of instrumental value in realizing whatever life plans the child may come to have. walter veit has argued that there is no intrinsic moral difference between 'creating' and 'choosing' a life, thus making eugenics a natural consequence of accepting the principle of procreative beneficence. disabilities in 2006, three percent of pgd clinics in the us reported having selected an embryo for the presence of a disability. couples involved were accused of purposely harming a child. this practice is notable in dwarfism, where parents intentionally create a child who is a dwarf. in the selection of a saviour sibling to provide a matching bone marrow transplant for an already existing affected child, there are issues including the commodification and welfare of the donor child. by relying on the result of one cell from the multi-cell embryo, pgd operates under the assumption that this cell is representative of the remainder of the embryo. this may not be the case as the incidence of mosaicism is often relatively high. on occasion, pgd may result in a false negative result leading to the acceptance of an abnormal embryo, or in a false positive result leading to the deselection of a normal embryo. another problematic case is the cases of desired non-disclosure of pgd results for some genetic disorders that may not yet be apparent in a parent, such as huntington disease. it is applied when patients do not wish to know their carrier status but want to ensure that they have offspring free of the disease. this procedure can place practitioners in questionable ethical situations, e.g. when no healthy, unaffected embryos are available for transfer and a mock transfer has to be carried out so that the patient does not suspect that he/she is a carrier. the eshre ethics task force currently recommends using exclusion testing instead. exclusion testing is based on a linkage analysis with polymorphic markers, in which the parental and grandparental origin of the chromosomes can be established. this way, only embryos are replaced that do not contain the chromosome derived from the affected grandparent, avoiding the need to detect the mutation itself. because of the sensitivity of the issue, as the above cases demonstrate, preimplantation genetic diagnosis has sparked a rich debate in academia and beyond one argument that is expressed by those who are against the possibility of discarding an embryo to avoid the risk of disability is that of "existence and nonexistence". that is, regarding the possible adverse selection of embryos that might develop "disabilities" such as deafness. according to this argument if the only two possible alternatives are "coming into the world" or "not coming into the world", granting them the right to come into the world is better than the alternative of not existing. another widely used argument for the rejection of the practice of "preimplantation genetic diagnosis" involves thinking about the meaning of the term "disability" (bickenach & chatterji, 2003). the argument in support of this idea is that "disability" is determined by the social construction regarding the idea of disability. on the one hand, the language of medicine describes disability as something whose functionalities deviate from a normal functioning. on the other hand, however, much of the disability community emphasizes that disability is often determined by the way society structures the world. a world made for a certain type of person. in this sense, these same people who highlight this message seek to emphasize the relativity of the concept of "normalcy" or "health". these depend on time, place, and society. in this light, then, the argument is that we should not avoid the birth of people with disabilities – through preimplantation genetic diagnosis – but we should give ourselves an answer to the question: how to decide what is a disability to allow pgd. on the other hand, regarding the arguments in favor of preimplantation genetic diagnosis, the literature mainly highlights three most common types of arguments the first type of argument is mainly made by a part of academia that believes that a disability/disorder likely implies a reduced probability of flowering for the unborn child. thus, this type of argument is generally related to the idea of opportunities related to an individual's life, opportunities that if taken can make an individual's life worth living the second most common type of argument in the literature deviates slightly from the one mentioned above in that it focuses primarily on the duties of parents in relation to the human flourishing of the individual. this argument feeds on the idea that parents have an obligation and responsibility to ensure that the unborn child has minimum living conditions that can be met. finally, a final category of argument is one that emphasizes the importance of bringing individuals with disabilities/disorders into the world with the consideration of how much they can contribute to the socioeconomic growth of society. or rather, this argument refers to the fact that these individuals would not be able to contribute to improving the status quo and well-being of society as a whole. intersex traits main article: genetic diagnosis of intersex pgd allows discrimination against those with intersex traits. georgiann davis argues that such discrimination fails to recognize that many people with intersex traits led full and happy lives. morgan carpenter highlights the appearance of several intersex variations in a list by the human fertilisation and embryology authority of "serious" "genetic conditions" that may be de-selected in the uk, including 5-alpha reductase deficiency and androgen insensitivity syndrome, traits evident in elite women athletes and "the world's first openly intersex mayor". organisation intersex international australia has called for the australian national health and medical research council to prohibit such interventions, noting a "close entanglement of intersex status, gender identity and sexual orientation in social understandings of sex and gender norms, and in medical and medical sociology literature". in 2015, the council of europe published an issue paper on human rights and intersex people, remarking: intersex people's right to life can be violated in discriminatory "sex selection" and "preimplantation genetic diagnosis, other forms of testing, and selection for particular characteristics". such de-selection or selective abortions are incompatible with ethics and human rights standards due to the discrimination perpetrated against intersex people on the basis of their sex characteristics. savior siblings pgd combined with hla (human leukocyte antigen) matching allows couples to select for embryos that are unaffected with a genetic disease in hopes of saving an existing, affected child. the "savior sibling" would conceivably donate life-saving tissue that is compatible to his/her brother or sister. some ethicists argue that the "savior siblings" created from this procedure would be treated as commodities. another argument against selecting for "savior siblings" is that it leads to genetically engineered "designer babies". this argument prompts a discussion between the moral distinction of enhancing traits and preventing