choroid plexus cyst, which are usually normal, but can be associated with an increased risk for chromosome abnormalities. other screening tests, such as the quad test, can also have false positives and false negatives. even when the quad results are positive (or, to be more precise, when the quad test yields a score that shows at least a 1 in 270 risk of abnormality), usually the pregnancy is normal, but additional diagnostic tests are offered. in fact, consider that down syndrome affects about 1:400 pregnancies; if you screened 4000 pregnancies with a quad test, there would probably be 10 down syndrome pregnancies of which the quad test, with its 80% sensitivity, would call 8 of them high-risk. the quad test would also tell 5% (~200) of the 3990 normal women that they are high-risk. therefore, about 208 women would be told they are high-risk, but when they undergo an invasive test, only 8 (or 4% of the high risk pool) will be confirmed as positive and 200 (96%) will be told that their pregnancies are normal. since amniocentesis has approximately a 0.5% chance of miscarriage, one of those 200 normal pregnancies might result in a miscarriage because of the invasive procedure. meanwhile, of the 3792 women told they are low-risk by the quad test, 2 of them will go on to deliver a baby with down syndrome. the quad test is therefore said to have a 4% positive predictive value (ppv) because only 4% of women who are told they are "high-risk" by the screening test actually have an affected fetus. the other 96% of the women who are told they are "high-risk" find out that their pregnancy is normal. by comparison, in the same 4000 women, a screening test that has a 99% sensitivity and a 0.5% false positive rate would detect all 10 positives while telling 20 normal women that they are positive. therefore, 30 women would undergo a confirmatory invasive procedure and 10 of them (33%) would be confirmed as positive and 20 would be told that they have a normal pregnancy. of the 3970 women told by the screen that they are negative, none of the women would have an affected pregnancy. therefore, such a screen would have a 33% positive predictive value. the real-world false-positive rate for the quad test (as well as 1st trimester combined, integrated, etc.) is greater than 5%. 5% was the rate quoted in the large clinical studies that were done by the best researchers and physicians, where all the ultrasounds were done by well-trained sonographers and the gestational age of the fetus was calculated as closely as possible. in the real world, where calculating gestational age may be a less precise art, the formulas that generate a patient's risk score are not as accurate and the false-positive rate can be higher, even 10%. because of the low accuracy of conventional screening tests, 5–10% of women, often those who are older, will opt for an invasive test even if they received a low-risk score from the screening. a patient who received a 1:330 risk score, while technically low-risk (since the cutoff for high-risk is commonly quoted as 1:270), might be more likely to still opt for a confirmatory invasive test. on the other hand, a patient who receives a 1:1000 risk score is more likely to feel assuaged that her pregnancy is normal. both false positives and false negatives will have a large impact on a couple when they are told the result, or when the child is born. diagnostic tests, such as amniocentesis, are considered to be very accurate for the defects they check for, though even these tests are not perfect, with a reported 0.2% error rate (often due to rare abnormalities such as mosaic down syndrome where only some of the fetal/placental cells carry the genetic abnormality). a higher maternal serum afp level indicates a greater risk for anencephaly and open spina bifida. this screening is 80% and 90% sensitive for spina bifida and anencephaly, respectively. amniotic fluid acetylcholinesterase and afp level are more sensitive and specific than afp in predicting neural tube defects. many maternal-fetal specialists do not bother to even do an afp test on their patients because they do a detail ultrasound on all of them in the 2nd trimester, which has a 97% detection rate for neural tube defects such as anencephaly and open spina bifida. performing tests to determine possible birth defects is mandatory in all u.s. states. failure to detect issues early can have dangerous consequences on both the mother and the baby. obgyns may be held culpable. in one case a man who was born with spina bifida was awarded $2 million in settlement, apart from medical expenses, due to the obgyn's negligence in conducting afp tests. no prenatal test can detect all forms of birth defects and abnormalities. prenatal genetic testing another important issue is the uncertainty of prenatal genetic testing. uncertainty on genetic testing results from several reasons: the genetic test is associated with a disease but the prognosis and/or probability is unknown, the genetic test provides information different than the familiar disease they tested for, found genetic variants have unknown significance, and finally, results may not be associated with found fetal abnormalities. richardson and ormond thoroughly addressed the issue of uncertainty of genetic testing and explained its implication for bioethics. first, the principle of beneficence is assumed in prenatal testing by decreasing the risk of miscarriage, however, uncertain information derived from genetic testing may harm the parents by provoking anxiety and leading to the termination of a fetus that is probably healthy. second, the principle of autonomy is undermined given a lack of comprehension resulting from new technologies and changing knowledge in the field of genetics. and third, the principle of justice raised issues regarding equal access to emerging prenatal tests. availability of treatments if a genetic disease is detected, there is often no treatment that can help the fetus until it is born. however, in the us, there are prenatal surgeries for spina bifida fetus. early diagnosis gives the parents time to research and discuss post-natal treatment and care, or in some cases, abortion. genetic counselors are usually called upon to help families make informed decisions regarding results of prenatal diagnosis. patient education researchers have studied how disclosing amniocentesis or chorionic villous sampling (cvs) results on a fixed date versus a variable date (i.e. "when available") affects maternal anxiety. systematic review of the relevant articles found no conclusive evidence to support issuing amniocentesis results as soon as they become available (in comparison to issuing results on a pre-defined fixed date). the researchers concluded that further studies evaluating the effect of different strategies for disclosing cvs results on maternal anxiety are needed. concerns from disability rights activists and scholars disability rights activists and scholars have suggested a more critical view of prenatal testing and its implications for people with disabilities. they argue that there is pressure to abort fetuses that might be born with disabilities, and that these pressures rely on eugenics interests and ableist stereotypes. this selective abortion relies on the ideas that people with disabilities cannot live desirable lives, that they are "defective," and that they are burdens, while disability scholars argue that "oppression is what's most disabling about disability." marsha saxton suggests that women should question whether or not they are relying on real, factual information about people with disabilities or on stereotypes if they decide to abort a fetus with a disability. societal pressures amniocentesis has become the standard of care for prenatal care visits for women who are "at risk" or over a certain age. the wide use of amniocentesis has been defined as consumeristic. and some argue that this can be in conflict with the right to privacy, most obstetricians (depending on the country) offer patients the afp triple test, hiv test, and ultrasounds routinely. however, almost all women meet with a genetic counselor before deciding whether to have prenatal diagnosis. it is the role of the genetic counselor to accurately inform women of the risks and benefits of prenatal diagnosis. genetic counselors are trained to be non-directive and to support the patient's decision. some doctors do advise women to have certain prenatal tests and the patient's partner may also influence the woman's decision.