Editing Prenatal testing (section)

=== Non-genetic prenatal testing ===
Parents need to make informed decisions about screening, diagnosis, and any actions to be taken as a result. Many screening tests are inaccurate, so one worrisome test result frequently leads to additional, more invasive tests. If prenatal testing confirms a serious disability, many parents are forced to decide whether to continue the pregnancy or seek an abortion. The "option" of screening becomes an unexpected requirement to decide. {{cn|date=February 2025}}

In some genetic conditions, for instance [[cystic fibrosis]], an abnormality can only be detected if DNA is obtained from the fetus. Usually an invasive method is needed to do this.{{citation needed|date=October 2017}}

Ultrasound of a fetus, which is considered a screening test, can sometimes miss subtle abnormalities. For example, studies show that a detailed 2nd-trimester ultrasound, also called a level 2 ultrasound, can detect about 97% of neural tube defects such as [[spina bifida]] {{Citation needed|date=June 2010}}. Ultrasound results may also show "soft signs," such as an [[Echogenic intracardiac focus]] or a [[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.{{Citation needed|date=October 2011}}

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.{{cn|date=February 2025}}

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%.{{cn|date=February 2025}}

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.{{cn|date=February 2025}}

Both [[Type I and type II errors|false positives]] and [[Type I and type II errors|false negatives]] will have a large impact on a couple when they are told the result, or when the child is born. [[Medical diagnosis|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 [[Alpha-fetoprotein|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.{{Citation needed|date=June 2007}}

Amniotic fluid [[acetylcholinesterase]] and [[Alpha-fetoprotein|AFP]] level are more [[Sensitivity (tests)|sensitive]] and [[Sensitivity and specificity|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.{{Citation needed|date=October 2021}} Failure to detect issues early can have dangerous consequences on both the mother and the baby. [[OBGYN]]s may be held culpable. In one case a man who was born with spina bifida was awarded $2&nbsp;million in settlement, apart from medical expenses, due to the OBGYN's negligence in conducting AFP tests.<ref name="Fibia2">{{Cite web|url=http://www.boothkoskoff.com/wp-content/uploads/2013/01/spina_bifida.pdf|title=Medical malpractice: Childbirth, failed to perform AFP test|access-date=September 1, 2013|archive-date=March 3, 2016|archive-url=https://web.archive.org/web/20160303182100/http://www.boothkoskoff.com/wp-content/uploads/2013/01/spina_bifida.pdf|url-status=dead}}</ref>

No prenatal test can detect ''all'' forms of birth defects and abnormalities.{{cn|date=February 2025}}