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Non-invasive prenatal genetic screening is typically performed at the end of the 1st trimester (11–14 weeks) or during the beginning of the second trimester (15–20 weeks). This involves the pregnant woman receiving a blood draw with a needle and a syringe and an ultrasound of the fetus.
The sex of the fetus may be discerned by ultrasound as early as 11 weeks' gestation. The accuracy is relatively imprecise when attempted early. [15] [16] [17] After 13 weeks' gestation, a high accuracy of between 99% and 100% is possible if the fetus does not display intersex external characteristics. [18]
Routine tests in the first trimester of pregnancy generally include: Complete blood count; Blood type. Rh-negative antenatal patients should receive RhoGAM at 28 weeks to prevent Rh disease. Indirect Coombs test (AGT) to assess risk of hemolytic disease of the newborn [5] Rapid plasma reagin test to screen for syphilis; Rubella antibody screen [6]
An amniocentesis is typically performed in the second trimester between the 15th and 20th week of gestation. [5] Women who choose to have this test are primarily those at increased risk for genetic and chromosomal problems, in part because the test is invasive and carries a small risk of pregnancy loss. [5]
The triple test, also called triple screen, the Kettering test or the Bart's test, is an investigation performed during pregnancy in the second trimester to classify a patient as either high-risk or low-risk for chromosomal abnormalities (and neural tube defects). The term "multiple-marker screening test" is sometimes used instead.
A positive test indicates an increased risk of preterm birth, and a negative test has a high predictive value. [35] It has been shown that only 1% of women in questionable cases of preterm labor delivered within the next week when the test was negative. [89]
There are two distinct measurements: the size of the nuchal translucency and the thickness of the nuchal fold. Nuchal translucency size is typically assessed at the end of the first trimester, between 11 weeks 3 days and 13 weeks 6 days of pregnancy. [3] Nuchal fold thickness is measured towards the end of the second trimester.
Typically, MSAFP is measured in the beginning of the second trimester (14–16 weeks). It may be measured alone or as part of a package of routine prenatal screening tests, such as a triple test or quad test. Because MSAFP test results must be interpreted according to the gestational age, they often are reported in terms of multiple of the ...