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Genetic Testing and Screening: I. Reproductive Genetic Testing

I. REPRODUCTIVE GENETIC TESTING

Reproductive genetic testing comprises a set of techniques for sample collection and analysis, the aims of which are to detect fetal anomaly. This article will describe the most important of these techniques and consider their bioethical aspects. This will include both those reproductive genetic technologies that are used in established pregnancies and preimplantation genetic diagnosis, performed before the establishment of a uterine pregnancy.

Methods for Obtaining Samples for Prenatal Diagnosis

Amniocentesis is frequently used synonymously with the term prenatal testing. Amniocentesis is in fact merely a technique for removal, via a needle puncture of the uterus, of amniotic fluid from the sac which surrounds the fetus during pregnancy. This fluid contains fetal cells on which analyses can be performed. The usefulness of amniocentesis is tightly linked to expanding knowledge about genetics, the development of techniques of fetal analysis, and changing legal and social norms.

In 1955, it was first demonstrated that fluid could be removed from the amniotic sac, that fetal cells could then be cultured, and that the total number of chromosomes—including the sex chromosomes—could be ascertained—a process called karyotyping. The first use of karyotyping was to identify male fetuses of women who carried serious genetic conditions on their X chromosome. However, this was initially of limited usefulness as no information other than fetal sex was obtainable, the safety of the procedure needed further investigation, and pregnancy termination for fetal anomaly was not legal.

The later finding that a karyotype showing three rather than two copies of a chromosome (trisomy 21) was indicative of Down syndrome presented the possibility of much broader use for amniocentesis. Not only was Down syndrome an important cause of mental retardation, it was also predicted by a pregnant woman's increasing age rather than by her genetic history. When, in the mid-1970s, a large study demonstrated the safety of amniocentesis (NICHD National Registry for Amniocentesis Study Group) at approximately the same time that the Supreme Court decision in Roe v. Wade made abortion legal in the United States, the way was opened to the population-based use of this technique for women of advanced maternal age.

Serious maternal complications from amniocentesis are rare; the primary medical risk of amniocentesis is fetal loss from the procedure. For this reason, the age, at which amniocentesis is routinely offered, is driven by an equation that looks for equipoise between the risk of procedure-related miscarriage and the age-related risk of Down syndrome. It is worth noting that one can infer from this equation an equivalence between the negative outcome of a fetal death and birth of a child with a disability, an equivalence which, as discussed below, would be contested from various positions critical of prenatal testing. Nevertheless, as rates of procedure-related miscarriage have decreased—due primarily to the use of real-time ultrasound to guide the needle—the age at which women are routinely offered amniocentesis has also decreased. At the beginning of the twenty-first century, it is standard of care to offer amniocentesis to women over age thirty-five.

Although amniocentesis is most closely associated with trisomy 21, any chromosomal abnormality can be detected through karyotyping, and the sample of fluid obtained can be used to diagnose any fetal anomaly for which a cytogenetic, biochemical, or DNA test has been developed (e.g., Tay-Sachs, sickle cell anemia, Huntington's disease).

EARLY AMNIOCENTESIS AND CHORIONIC VILLUS SAMPLING. Amniocentesis is performed in the middle of the second trimester of pregnancy. By this time, pregnant women have often experienced quickening (perceived fetal movement) and the fetus is nearing the age of viability. These factors have led to a search for earlier modes of fetal sample collection, including first trimester ("early") amniocentesis and chorionic villus sampling (CVS).

Although there was initial enthusiasm for early amniocentesis performed in the eleventh through thirteenth weeks of pregnancy, recent data suggest that this procedure may pose significantly greater fetal risks than traditional amniocentesis, including high rates of pregnancy loss and risk of fetal malformations (e.g., club foot) (Bianchi, 2000). In addition, early amniocentesis is more technically difficult and thus more often will fail to obtain a fluid sample adequate for cell culture. Enthusiasm for the procedure has waned, although it is possible that future solutions to these problems will revitalize interest.

Rather, it is CVS that appears likely to become the procedure of choice for earlier fetal sample collection. The chorionic villi are precursors of the placenta and have proved a good source of fetal tissue. CVS can be performed safely as early as the tenth week of pregnancy, either transabdominally or transvaginally; the risks have been found to compare well with second trimester amniocentesis (Bianchi, 2000). In addition, the waiting period for results following CVS is shorter than in amniocentesis—three to eight rather than ten to fourteen days. Since there is considerable documented anxiety for parents waiting for prenatal test results, this represents a significant advantage.

MATERNAL SERUM FETAL CELL RECOVERY. Both CVS and amniocentesis are invasive techniques. They share disadvantages of potential fetal harm and are relatively costly to perform. Thus, there continues to be interest in finding a non-invasive, less expensive technique that could be used to gather a fetal sample early in pregnancy. There is only one such technique on the horizon in 2003—maternal serum fetal cell recovery.

It is known that a small number of fetal cells are sloughed off and cross into maternal blood circulation. After isolation from a maternal blood draw, these cells can then be used for any desired fetal analysis. However, fetal cells are numerically rare in maternal blood and their identification and isolation is difficult. In addition, the type of cell most amenable to detection and isolation is not ideal for chromosomal analysis (Holzgreve and Hahn). Nevertheless, work on this technique progresses and a prospective multi-center trial of this technique as a screen for chromosomal anomalies began in the mid-1990s (Bianchi, 2002). Early results were promising for chromosome analysis, but the future goal of fetal cell recovery remains broader than this: To be able to perform not only analysis of chromosomal abnormalities, but to capture the larger number of fetal cells needed for DNA techniques. This goal holds the promise of genetic analysis for any disorder of interest.

Screening Tests and Diagnostic Tests

The above techniques are used for diagnosis in high-risk women. But almost all pregnant women are offered a variety of other prenatal screening tests.

Although the distinction quickly becomes complicated, in its simplest form, screening tests are offered to a population of apparently healthy persons in order to find those few at increased risk. Ideally, screening tests are easy and inexpensive to perform and interpret, and do not entail risk for the person screened. Screening tests have high rates of initial positive results and thus a large percentage of people who have positive screening tests will prove not to have the screened-for problem on follow-up diagnostic testing.

In contrast, diagnostic tests are offered to individuals known to be at increased risk of a condition in order to answer the question, "Does this person have this disease?" Diagnostic tests are generally more complicated and expensive to perform and interpret, and may entail risk. They are expected to have higher standards of sensitivity and specificity: to do a much better job at identifying all and only cases of the disorder.

The screening and diagnostic testing regimens typically offered to pregnant woman and couples at the beginning of the twenty-first century are presented in Table 1. Each begins by asking a question that assigns the woman to a risk level. It is important to realize that each screening test has its own percentage of initial positive results; thus, each additional screen raises the risk for any individual woman of getting an initial positive result at some time during pregnancy. In addition, these tests are not all done at the same time in pregnancy. For example, an African-American woman, less than thirty-five years old, would be offered carrier testing for sickle cell disease in her first trimester and would also be offered multiple marker screening in her second trimester.

MSAFP and Multiple Marker Screening

While amniocentesis for Down syndrome is perhaps better known, the test which truly revolutionized prenatal diagnosis was maternal serum alpha fetoprotein (MSAFP) screening, which became the first screening test offered to all pregnant women solely for the purpose of discovering risk for a fetal anomaly.

MSAFP screening was developed to detect neural tube defects (NTDs) in the fetus. NTDs comprise a set of defects involving the development of the brain and spine and leading to varying degrees of physical and cognitive impairment, some of which are incompatible with life; they are among the most common of serious birth defects. Finding fetal NTDs is complicated by the fact that over 90 percent occur to women at no known risk, making it necessary to offer testing to the entire population of pregnant women to detect any reasonable percentage of fetal NTDs.

Alpha fetoprotein is a substance produced by the developing fetus and present in maternal blood during pregnancy. In the early 1970's, it was found that higher than normal levels of MSAFP correlated with increased risk of fetal NTDs. This suggested the possibility of an inexpensive, minimally invasive, screening modality for NTDs (Brock, Bolton, and Monaghan).

In the 1980's, researchers linked lower than normal levels of MSAFP to Down syndrome and other chromosomal abnormalities, thus expanding the utility of the test (Merkatz, Nitowsky, Macri, et al.). Early pilot projects demonstrating the feasibility of MSAFP testing increased enthusiasm for it as a prenatal screening test, and the screening became firmly established as standard of care in the United States when an American College of Obstetrics and Gynecology "Legal Alert" warned obstetrical providers that failure to offer the test might leave them open to liability in the case of a baby born with a detectable anomaly (ACOG, 1985).

However, one concern about using MSAFP to detect Down syndrome was that it had much lower sensitivity and specificity for chromosomal abnormalities that it did for NTDs. When it was found that the addition of other biochemical markers improved the ability of the screen to predict Down syndrome, these quickly became added to the analysis. Most providers perform multiple marker screening, with a triple marker screen including human chorionic gonadotrophin and unconjugated estriol being the most common. Since all these analytes are gathered from the same

TABLE 1

Current Screening Practices
Screening
question
Answer Next Step Next Step Next Step
What is your age?>35Referral for amniocentesis/CVS
Is there any genetic
disorder in your family?
YesReferral for carrirer testing or
amniocentesis/CVS
(Depending on characteristics of
the disorder and the mode of
genetic transmission)
What is the race/ethnicity/country of origin of woman (and partner)?African-AmericanOffered sickle cell carrier testingIf both partners are
carriers, referral for
amniocentesis/CVS
Ashkenazi-JewishOffered Tay-Sachs (and possibly
an Ashkenazi-Jewish panel,
including, e.g. Canavan disease)
carrier testing
If both partners are
carriers, referral for
amniocentesis/CVS
Southeast
Asian, Greek
Southern Italian
Standard blood work-up looking
for anemia may be used to
suggest need for a next step
Offered alpha or
beta thalassemia
carrier testing
If both partners are
carriers, referral for
amniocentesis/CVS
European-AmericanOffered cystic fibrosis carrier
testing; some places may make
this offer to ALL pregnant women
If both partners are
carriers, referral for
amniocentesis/CVS
Are you beginning
prenatal care <16
weeks of pregnancy
YesOffered multiple marker screeningIf result is positive
HIGH, referred for ultrasound
If result is
inconclusive, referred
for
If result is positive
LOW, referred for amniocentesis
Suggested one-age screening protocol
Are you beginning
prenatal care in
the first trimester?
YesOffered PAPP-A screening,
adjusted by maternal age, and
ultrasound to assess fetal nuchal translucency
If joint results are
positive, referred for amniocentesis
SOURCE: Author.

blood sample, the test has not changed from the point of view of the pregnant woman.

One important aspect of multiple marker screening is that it cannot be done until the fifteenth week of pregnancy, and most women are screened at sixteen weeks and above. This means that diagnostic work-up for a positive test is done toward the end of the second trimester, and a woman who wanted to terminate a pregnancy based on the results of a diagnostic test would be facing a late second trimester termination.

Suggestions for a One-Age Screening Protocol

Since the 1970s, maternal age has been used as a screen for offering amniocentesis to pregnant women, with biochemical screening offered to younger women since the late 1980s.

However, there is debate about these guidelines (see, for example, Rosen, Kedar, Amiel, et al.; Haddow, Palomaki, Knight, et al.; Pauker and Pauker; Egan, Benn, Borgida, et al.; Dommergues, Audibert, Benattar, et al.). This controversy seems to be based largely on the trend toward women bearing children at later ages (from 1974 to 1997, the United States has seen a 2.7-fold increase in live births among women ages 35–49) (Egan, et al.). This age increase means a dramatic increase in the number of amniocenteses performed, with concomitant procedure-related losses and economic costs.

The most radical suggestion for changing the routine is to screen women of all ages in an identical manner (see last row of Table 1). The most promising of such approaches include ultrasound measurement of the thickness of subcutaneous edema in the neck of the fetus (fetal nuchal translucency) combined with new types of serum marker screening (e.g., PAPP-A). When these techniques are performed in the first trimester of pregnancy, and the results are combined with the risk based on maternal age alone, this regimen is believed to have an 80 to 90 percent detection rate for trisomy 21 and other chromosomal abnormalities (Nicolaides, Heath, and Liao). Although fetal nuchal translucency screening has not been accepted as standard of care, the American College of Obstetrics and Gynecologists stated at the end of the twentieth century that it shows promise (1999).

The advantages of a single screening modality for women of all ages are that it would decrease the number of amniocenteses in older women and, with these more sensitive screening modalities, also increase the detection rate in younger women. (In terms of raw numbers, younger women have the greatest number of affected pregnancies.) Several sets of modeling data suggest that with this approach the overall detection rate would improve and the fetal loss rates would decrease (Rosen, Kedar, Amiel, et al.; Haddow, Palomaki, Knight, et al.; Dommergues, Audibert, Benattar, et al.). The disadvantage, however, would be that, since amniocentesis has a virtual 100 percent sensitivity, some fetuses with Down syndrome that would have been detected through universal screening of women over thirty-five would be missed, and some women over thirty-five would bear a child with Down syndrome who would not otherwise have done so. The ethical, and political, debates concern the fact that a medical service that was accepted as a right for pregnant women of a certain age would be withheld from those same women unless they had demonstrated risk. This may well appear to be an unacceptable form of sudden healthcare rationing to older pregnant women.

It is also worth noting that none of these one-age screening models refer to the detection of neural tube defects, but rather appear to exist in a separate universe of consideration and calculation. Thus, they would not solve the problem of multiple screenings and multiple chances for initial positive results and concomitant anxiety.

Prenatal Screening and the Experience of Pregnancy

The advent of MSAFP screening transformed the experience of pregnancy for the low risk woman—that is, the great majority of pregnancies. As is clear from Table 1, it is possible for a woman to go through a period of waiting for results of one test only to then begin all over again with testing for another condition. For example, a thirty-year old Southeast Asian woman might have a standard blood workup that revealed anemia, be offered thalassemia carrier testing along with her partner, and, when both proved to be carriers, be offered CVS; she might have a negative result and then, some weeks later, be offered multiple marker screening and receive a positive result; she might then choose to undergo amniocentesis. All of this could produce a healthy baby and a disastrously upsetting and expensive pregnancy. There appear to be no empirical data on the frequency of such experiences. However, variations on this theme are frequently reported by obstetric providers.

General Ethical Issues in Prenatal Diagnosis

In addition to the issues involved in one mode of screening or another, there are overarching ethical issues that concern the entire project of prenatal diagnosis. These involve contestations over the meaning, experience, and implications of these tests. Specifically, there is a lack of clarity about the centrality of pregnancy termination to an offer of prenatal testing; whether testing resolves or creates maternal anxiety; and the relationship of individual reproductive choices to societal effect. This latter includes the effects of prenatal testing on those with disability and, more broadly, the relationship between prenatal screening programs and eugenics. Related to the latter is a question about the effectiveness of individual autonomous choice as a safeguard against eugenic abuses related to prenatal testing. All these issues affect and are affected by the lack of a mechanism for rational deliberative decision-making in the United States about why and which prenatal tests are developed and offered.

PRENATAL TESTING AND ABORTION DECISION MAKING. The performance of any medical test is predicated on a hypothesis of benefit which defines the way in which the results of the test will lead to actions that help prevent disease or ameliorate its burden. Implicitly, the person whose disease burden is being ameliorated is the person being tested. Although it is everyone's hope that identification of a fetus with a particular condition will lead to prevention or cure of that disease, this is very rarely true today and the only way to prevent the fetus being born with the condition is through termination of the pregnancy.

Religious objections. From the viewpoint of conservative religious positions that object to abortion under all circumstances, the link of prenatal testing and abortion is clear, and offering women this choice is deeply objectionable.

Cost benefit literature. There is another body of literature in which the centrality of abortion decision making to prenatal testing is quite clear—literature that assesses the effectiveness of testing programs by comparing the economic costs of prenatal testing to economic savings. The costs include such items as sample collection, analysis, and results communication; savings include monies not spent on medical care for children who would have been born with disability but instead are not born. One of the major variables in the equation is the minimum number of women who need to choose termination in order for the screening program to be cost-effective, assuming that not all women who test positive will go on to end the pregnancy. Thus, the calculation both acknowledges the autonomous choice involved in prenatal screening programs in the United States and the need for those autonomous choices to lean, in sum, in the direction of pregnancy termination.

However, most literature that discusses the benefits of prenatal testing talks about the reassurance provided about the health of the fetus for the large majority of women—those who test negative—and the chance for women or couples who choose not to terminate to prepare emotionally for the birth of child with a disability. Generally stated last is the enhancement of reproductive choice in the case of a positive test result.

REASSURANCE AND ANXIETY. The issue of reassurance and, conversely, anxiety in relation to prenatal testing has received considerable attention. Women themselves often cite reassurance as a benefit of testing. Much empirical research has focused on the issue of anxiety for that group of women who receive an initial positive result. These data suggest that women's anxiety is raised following a positive result but that, in general, this anxiety is relieved by a negative result. Data suggest that for some women, however, the anxiety persists, along with difficulty believing their fetus is healthy.

Some feminist critics also suggest an irony in which the reassurance provided by testing may be necessary, in great part, due to anxiety raised by the testing itself. In general, these critics claim that the expansion of prenatal testing has radically changed the experience of pregnancy and that while the number of fetal anomalies has, of course, not increased, the perception of risk among pregnant women has increased greatly.

INFORMATION PROVISION. Another aspect of prenatal testing, sometimes cited by theoretical literature and pregnant women as an advantage for those unwilling to terminate a pregnancy, is the opportunity to have time to prepare emotionally for the birth of a child with a disability. However, there are no empirical data demonstrating that advance preparation actually has an effect on adjustment to the birth of a child with a disability. In addition, the majority of women who receive positive results do terminate their pregnancies. Data suggest that close to 90 percent of women terminate following a diagnosis of a chromosomal disorder such as trisomy 21; the rate of termination for NTDs is more variable, reflecting the greater variation in the severity of the detected anomaly (Cragan, Roberts, Edmonds, et al.).

Thus, the most obvious advantage of prenatal testing must remain the ability to terminate a pregnancy which would result in a child with a disability. This suggests that the bifurcated conversation in the United States about prenatal testing—in which cost effectiveness calculations make assumptions which are omitted or contradicted in the clinical literature and most patient education materials—may make it difficult to have a societal conversation about the larger effects of prenatal testing on society.

The Effects of Individual Reproductive Choices on Society

In addition to advantageous or deleterious effects on individual women and couples, concerns exist about the effects of prenatal testing on society.

THE DISABILITY CRITIQUE. The most forceful critique of prenatal testing is that made by disability theorists (Parens and Asch). Their most straightforward claim is that prenatal testing represents "search and destroy" missions against those who would be born with disability and is, simply, a eugenic program. A more subtle disability critique states that the choice to abort an otherwise desired fetus on the basis of one trait or characteristic sends the message that the lives of those with disability are not valuable and that the disability makes the child unacceptable (Asch and Geller); this has been termed the expressivist argument. Objections to the expressivist argument share a skepticism about the ability of individual acts to constitute a message. Objections to the disability critique in general often point to the increasing societal protections of individuals with disability that have co-occurred with the growth of prenatal testing.

THE LIMITS OF AUTONOMY. The argument that prenatal testing is not eugenic and not disvaluing of living individuals with disability rests largely on the way that testing programs protect the autonomy of women's or couple's decisions in regard to the use of testing and test results. A central ethical issue, therefore, concerns the actuality and the limits of such autonomy. Specifically: Are women or couples making autonomous decisions in regard to prenatal testing? Can the aggregate effect of autonomous choices be eugenic? And, if they can, how problematic is this?

Are prenatal testing decisions truly autonomous? Individual autonomy is a foundational principle in Western bioethics, and there is virtually universal agreement that women and/or couples should make informed decisions about the use of testing and should not be coerced into pregnancy terminations following a positive prenatal test. The disagreement that exists, therefore, is about the possibility and actuality of such autonomy.

On a narrow level, there is concern that women do not understand the implications of an offer of prenatal testing; this has led to attempts to improve the informed consent process. Yet empirical research suggests that such attempts are only partly successful in the prenatal testing arena, as is true of informed consent in general. Empirical data suggest that, especially low risk women who are offered prenatal testing in a context of routine prenatal care, are likely to conflate prenatal testing for fetal anomalies with tests which can directly benefit themselves and their fetus (Press and Browner). It is possible that this misunderstanding is enabled by healthcare providers who are likely to find greater liability risk in the woman who refuses testing and has a baby born with a disability than one who does not fully understand the implications of prenatal screening and participates regardless; it may also reflect a reluctance on the part of both providers and pregnant women to discuss pregnancy termination. Some critics suggest, however, that some women would not have started down the prenatal testing path if they had truly understood the implications in terms of pregnancy termination; they argue that this may represent a compromise of their autonomy.

A broader concern is that the very existence of large-scale prenatal testing compromises the possibility of individual autonomous decision making. Feminist critics, among others, point out that prenatal screening has become routinized, with an offer of some sort of prenatal screening standard of care for all pregnant women. These critics assert that in this setting, not being screened, while a possible choice, becomes a marked one that requires justification to one's healthcare providers and one's peers. Concern has also been expressed that mothers who decide to forgo testing and give birth to a child with a disability will be blamed by society and even, perhaps, denied healthcare insurance for the child. There is little empirical support at this time for these latter claims.

Can the aggregate impact of autonomous choices be eugenic? Even if each choice to use prenatal testing and terminate a pregnancy is informed and autonomous, the net effect might be considered eugenic. And, in fact, there are those who do not consider this to be problematic. Thus, for example, some public health statements clearly cite the measure of success of screening for neural tube defects as the lowering of the number of children born with these defects. Some bioethicists also suggest that eugenics, premised on individual, autonomous choices, is not necessarily bad.

How Are Decisions About Prenatal Test Offers Made?

These positions would seem to require a clear social consensus of what changes in the gene pool would be eu-genic. Yet, at the turn of the twenty-first century there exists no body in the United States, as there is in other countries, that decides on the available panel of prenatal tests. Nor is there a forum for public discussion of this issue. Some tests stumble into becoming standard of care due to medico-legal concerns (e.g., MSAFP testing). At other times, decisions are made on an ad hoc bases. Thus, a strongly perceived need by obstetric providers for guidance about cystic fibrosis (CF) screening led to the convening of an National Institutes of Health (NIH) Consensus Development Conference. This group recommended the routine offer of CF carrier screening in pregnancy, but concerns that physicians were not prepared for this change in practice led to the creation of an ad hoc panel charged with creating recommended protocols for implementation (National Institutes of Health Consensus Development Conference). The existence of the panel has not calmed concerns that physicians are not ready to meet the challenge of offering a new population-based test.

As genes for Mendelian disorders and those that confer susceptibility to more common disorders are found in increasing numbers, the lack of any orderly process from gene discovery to test development and then to making that test available to the public becomes increasingly problematic. At this point, healthcare providers are the de facto gatekeepers, relying on recommendations from professional organizations, actions of insurance payers, patient demand, and their own consciences in making decisions about what tests to offer. As genetic knowledge increases, this will become an ever more pressing societal problem.

Preimplantation Genetic Diagnosis

If prenatal testing is about which children will not be born, preimplantation genetic diagnosis (PGD) can be said to be about which children will be born.

PGD began as an alternative to prenatal testing for fertile couples known to be at high risk of genetic disease. It comprises a series of highly technical steps. The scenario involves inducing superovulation in the woman to increase the number of eggs in one reproductive cycle, the harvesting of those eggs, and the creation of six to eight embryos by invitro fertilization (IVF). In the most common protocol, the resulting embryos are allowed to develop until they reach the eight- to twelve-cell stage, and then one or two cells are removed from each embryo for genetic analysis. Those embryos that carry the genetic defect are discarded. Depending on the number of unaffected embryos, some or all are implanted. Which embryos are chosen and what happens to those that remain are issues of ethical contention.

Many issues raised by PGD are outside the scope of this article. However, two issues raised by PGD are also directly related to dilemmas discussed in the context of prenatal diagnosis: First, what is abortion? Second, how does one decide which babies will be born, and with what traits and/or diseases?

WHAT IS ABORTION? One of the advantages commonly cited for PGD is that it avoids the problem of abortion. This assumes a definition of abortion as the interruption of an established pregnancy. However, abortion can also be defined as "the arrested development of an embryo at a more or less early stage" (from the Random House Dictionary of the English Language), a definition which would include the discarding of embryos, affected or unaffected, within PGD. It would also appear that those individuals (and points of view) most uncomfortable with abortion in the prenatal setting would be most likely to endorse this broader definition of abortion and thus be unlikely to see PGD as a solution to the abortion issue.

WHICH BABIES WILL BE BORN? PGD involves an issue not raised by prenatal diagnosis—more embryos are produced by PGD than can be used. The existence of these "excess embryos" demands that criteria be found on which to predicate decisions about which children should be born. Although, in practical terms, these decisions are often made on the basis of simply finding sufficient unaffected embryos for implantation, the possibility of deciding which embryos to implant has provoked considerable discussion. For example, is it appropriate to base a decision about which of two unaffected embryos to implant based on the preference of the parents for a child of one sex rather than the other?

Some of the discussion of how to choose embryos for implantation has a proscriptive edge, such as the view that to bring to birth a child with any impairment, however slight, if it could have been avoided, is to harm the child; more categorical is the view that procreative beneficence demands the selection of the "best" children. The logical extreme of this latter position is suggested by the view that "the question is not which individuals have worthwhile lives, but which of two possible worlds would be better: a world where disabled individuals are brought to birth or a world where nondisabled individuals are brought to birth" (Bennett, p. 468).

Much of this sort of discussion belies a belief in the ability of genetic analysis to do things that are neither currently possible nor likely to be so in the future—for example, to isolate the embryo that will become the most intelligent child. Nevertheless, these openly eugenic views, which are not found in the literature on prenatal testing, would appear to be premised on the belief that abortion is not involved in PGD and that the choice involves a more acceptable selection for rather than selection against. However, such an assumption would likely not satisfy those who have the most concerns about abortion. And for those critics (see, for example, the feminist and disability critiques) whose concerns do not involve abortion, this discussion around PGD lays bare the eugenic thrust they see in all prenatal testing.

Conclusion

Discussions of both prenatal testing and preimplantation genetic diagnosis appear to assume that the continuing march of reproductive technology is inevitable. It is possible that the overriding issue in all of reproductive genetics is whether society will see the development and use of these techniques as matter for democratic deliberation and decision, or whether the implementation of new technologies will continue in the established piecemeal fashion, and ethical discussion will continue to be reactive.

nancy press

kiley ariail

SEE ALSO: Abortion; Cloning: Reproductive; Disability; Embryo and Fetus; Eugenics; Eugenics and Religious Law; Genetic Counseling, Ethical Issues in; Genetic Counseling, Practice of; Genetic Discrimination; Maternal-Fetal Relationship; Mistakes, Medical; Moral Status; Reproductive Technologies;Value and Valuation; and other Genetic Testing and Screening subentries

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