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Maternal serum AFP (MSAFP) varies by orders of magnitude during the course of a normal pregnancy. MSAFP increases rapidly until about 32 weeks gestation, then decreases gradually. After the pregnancy ends it decreases rapidly, with a half-life of about 5 days. Typically, MSAFP is measured in the beginning of the second trimester (14–16 weeks).
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.
The available blood tests from the first trimester screen can test for plasma protein A and human chorionic gonadotropin. The second trimester screen looks at specific blood markers, to include the estriol, inhibin and human chorionic gonadotropin hormones and often consists of Alpha-fetoprotein (AFP) screening.
Alpha-fetoprotein (AFP, α-fetoprotein; also sometimes called alpha-1-fetoprotein, alpha-fetoglobulin, or alpha fetal protein) is a protein [5] [6] that in humans is encoded by the AFP gene. [ 7 ] [ 8 ] The AFP gene is located on the q arm of chromosome 4 (4q13.3). [ 9 ]
The first documented use of PUBS came in 1983 by Daffos and colleagues who sampled blood from an umbilical vein with a needle and monitored its maneuvers with an ultrasound. [7] PUBS has presented a more successful and less dangerous alternative to fetoscopy, which had a miscarriage risk of 5-10%. [ 2 ]
As an example, Alpha-fetoprotein (AFP) testing is used to screen for a neural tube defect (NTD) during the second trimester of pregnancy. If the median AFP result at 16 weeks of gestation is 30 ng/mL and a pregnant woman's AFP result at that same gestational age is 60 ng/mL, then her MoM is equal to 60/30 = 2.0.
In oncology, AFP-L3 is an isoform of alpha-fetoprotein (AFP), a substance typically used in the triple test during pregnancy and for screening chronic liver disease patients for hepatocellular carcinoma (HCC).
The use of ultrasound and biochemical markers to detect aneuploidies is usually done in the first and / or second trimester of pregnancy. [8] Aneuploidies is when a fetus retains an abnormal amount of haploid cells from their parents. However, both of these approaches have a high rate of false positive results of 2–7%. [9]