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 Down syndrome 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 Down syndrome 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 Down syndrome. Ultrasound
Ultrasound imaging can be used to screen for Down syndrome. 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 Down syndrome picking up 75–80% of cases and being falsely positive in 6%. Blood tests
Several blood markers can be measured to predict the chances of Down syndrome during the first or second trimester. Testing in both trimesters is sometimes recommended and test results are often combined with ultrasound results.
Hydrometra is a genus of water measurers in the family Hydrometridae. There are more than 120 described species in Hydrometra. See also
List of Hydrometra species

References
Further reading


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