Triple test

The most common abnormality the test can screen is trisomy 21 (Down syndrome). In addition to Down syndrome, the triple and quadruple screens assess risk for fetal trisomy 18 also known as Edwards syndrome, open neural tube defects, and may also detect an increased risk of Turner syndrome, triploidy, trisomy 16 mosaicism, fetal death, Smith–Lemli–Opitz syndrome, and steroid sulfatase deficiency. ==Values measured==

The triple test measures the following three levels in the maternal serum: • alpha-fetoprotein (AFP) • human chorionic gonadotropin (hCG) • unconjugated estriol (UE3) ==Interpretation==

The levels may indicate increased risk for certain conditions or may be benign: An estimated risk is calculated and adjusted for the expectant mother's age; if she is diabetic; if she is having twins or other multiples, and the gestational age of the fetus. Weight and ethnicity may also be used in adjustments. Many of these factors affect the levels of the substances being measured and the interpretation of the results: The test is for screening, not for diagnosis, and does not have nearly the same predictive power as that of genetic blood testing (testing cell-free fetal DNA, or invasive genetic testing which are performed by amniocentesis or chorionic villus sampling. The screening test carries a much lower risk to the fetus than invasive testing, however, and in conjunction with the age-related risk of the patient it is useful to help determine the need for more invasive tests. ==Variations==

If only two of the hormones above are tested for, then the test is called a double test. A quad test tests an additional hormone, inhibin. Furthermore, the triple test may be combined with an ultrasound measurement of nuchal translucency. Double test Free beta hCG and PAPP-A are measured. However, the maternal age, weight, ethnicity etc. are still included. In the UK the double test is part of the combined test for prenatal diagnostics. Quadruple test A test of levels of dimeric inhibin A (DIA) is sometimes added to the other three tests, under the name "quadruple test." Other names used include "quad test", "quad screen", or "tetra screen." Inhibin A will be found high in cases of trisomy 21 and unchanged in cases of trisomy 18. ==See also==