Before birth When screening tests predict a high possibility of<unk> , a more invasive diagnostic test (amniocentesis or chorionic villus sampling) is needed to confirm the diagnosis. The false-positive rate with screening is about 2–5% (see section Screening below). Amniocentesis and chorionic villus sampling are more reliable tests, but they increase the risk of miscarriage by between 0.5 and 1%. The risk of limb problems may be increased in the offspring if chorionic villus sampling is performed before 10 weeks. The risk from the procedure is greater the earlier it is performed, thus amniocentesis is not recommended before 15 weeks gestational age and chorionic villus sampling before 10 weeks gestational age. Abortion rates About 92% of pregnancies in Europe with a diagnosis of<unk>  are terminated. As a result, there is almost no one with<unk>  in Iceland and Denmark, where screening is commonplace. In the United States, the termination rate after diagnosis is around 75%, but varies from 61% to 93% depending on the population surveyed. Rates are lower among women who are younger and have decreased over time. When asked if they would have a termination if their fetus tested positive, 23–33% said yes, when high-risk pregnant women were asked, 46–86% said yes, and when women who screened positive are asked, 89–97% say yes. After birth The diagnosis can often be suspected based on the child's physical appearance at birth. An analysis of the child's chromosomes is needed to confirm the diagnosis, and to determine if a translocation is present, as this may help determine the chances of the child's parents having further children with<unk> . Parents generally wish to know the possible diagnosis once it is suspected and do not wish pity. Screening Guidelines recommend screening for<unk>  to be offered to all pregnant women, regardless of age. A number of tests are used, with varying levels of accuracy. They are typically used in combination to increase the detection rate. None can be definitive, thus if screening is positive, either amniocentesis or chorionic villus sampling is required to confirm the diagnosis. Screening in both the first and second trimesters is better than just screening in the first trimester. The different screening techniques in use are able to pick up 90–95% of cases, with a false-positive rate of 2–5%. If<unk>  occurs in one in 500 pregnancies with a 90% detection rate and the test used has a 5% false-positive rate, this means, of 26 women who test positive on screening, only one will have<unk>  confirmed. If the screening test has a 2% false-positive rate, this means one of eleven who test positive on screening have a fetus with<unk> . + First- and second-trimester screening Screen Week of pregnancy when performed Detection rate False positive Description Combined test 10–13.5 wks 82–87% 5% Uses ultrasound to measure nuchal translucency in addition to blood tests for free or total beta-hCG and PAPP-A Quad screen 15–20 wks 81% 5% Measures the maternal serum alpha-fetoprotein, unconjugated estriol, hCG, and inhibin-A Integrated test 15–20 wks 94–96% 5% Is a combination of the quad screen, PAPP-A, and NT Cell-free fetal DNA From 10 wks 96–100% 0.3% A blood sample is taken from the mother by venipuncture and is sent for DNA analysis. Ultrasound Ultrasound imaging can be used to screen for<unk> . Findings that indicate increased chances when seen at 14 to 24 weeks of gestation include a small or no nasal bone, large ventricles, nuchal fold thickness, and an abnormal right subclavian artery, among others. The presence or absence of many markers is more accurate. Increased fetal nuchal translucency (NT) indicates an increased possibility of<unk>  picking up 75–80% of cases and being falsely positive in 6%. File:T21.Ultrasound of fetus with<unk>  showing a large bladder File:Nuchal edema in<unk>  Dr. W. Moroder.Enlarged NT and absent nasal bone in a fetus at 11 weeks with<unk>  Blood tests Several blood markers can be measured to predict the chances of<unk>  during the first or second trimester. Testing in both trimesters is sometimes recommended and test results are often combined with ultrasound results. In the second trimester, often two or three tests are used in combination with two or three of: α-fetoprotein, unconjugated estriol, total hCG, and free βhCG detecting about 60–70% of cases. Testing of the mother's blood for fetal DNA is being studied and appears promising in the first trimester. The International Society for Prenatal Diagnosis considers it a reasonable screening option for those women whose pregnancies are at a high likelihood of trisomy 21. Accuracy has been reported at 98.6% in the first trimester of pregnancy. Confirmatory testing by invasive techniques (amniocentesis, CVS) is still required to confirm the screening result.
Down syndrome
Alzheimer's disease
Baboon syndrome
Apert syndrome
Ring chromosome 14 syndrome
Ring chromosome 20 syndrome
TORCH syndrome
Williams syndrome