Human chorionic gonadotropin (hCG) is exclusively made by the outer most part of the placenta.It may be measured independently or can be a part of a combined screen with other serum markers. AFP is produced by the fetal liver and yolk sac and can assess for open neural tube defects and ventral wall defects in the heart. Interestingly, it was the first maternal serum biomarker that became available in the 1980s. Alpha-fetoprotein (AFP) can be measured in the second trimester, typically between 15.0-22.6 weeks of gestation.Several biomarkers have been identified, researched, validated, and commercialized as maternal serum screening tests: There was a need for a non-invasive, inexpensive, reliable pregnancy screening method that could be incorporated into routine prenatal care. Prior to prenatal screening, maternal age alone was used to assess for fetal aneuploidy, which had a low sensitivity of only about 30%. Women who are 35 years or older at delivery, are considered “high risk” for aneuploidies. The most common chromosome conditions are Down syndrome (trisomy 21) Edwards syndrome (trisomy 18) Patau syndrome (trisomy 13) Turner syndrome (monosomy X) and Klinefelter syndrome (XXY). The word “trisomy” refers to an extra chromosome where there are three copies of a chromosome rather than the typical pair of chromosomes, and “monosomy” describes a missing chromosome where there is only one copy. Most aneuploidies are lethal, but some may make it to term. These are usually aneuploidies – the addition or subtraction of an entire chromosome. The chance for a pregnancy to be affected with a chromosomal condition increases with maternal age. Similarly, women who have average-risk pregnancies may opt in for diagnostic testing. Some women with high-risk pregnancies may decline diagnostic testing. Not all pregnancies that are classified as high risk have a fetus with a birth defect or genetic condition (this would be a false positive screening result) and not all affected pregnancies will be in the high-risk group (false negative). Following a positive screening test, further diagnostic tests may be recommended. The nature of screening means there will be false positive and false negative risks determined however, the idea is to keep those false results to an acceptable minimum rate Prenatal screening should not be repeated if there is an informative result. Prenatal screening provides a probability that a particular condition exists. Screening is not diagnostic testing and a screening test cannot provide a definitive diagnosis. ![]() The purpose of prenatal screening is to put the pregnancy into a risk category that a particular condition that could affect the fetus exists, i.e., increased risk or no increased risk. ![]() What is the Purpose of Prenatal Screening? The aim of this article is to review the history of prenatal screening and current technologies available. Technologies used in prenatal screening have rapidly expanded and increased in accuracy over the last several decades. Prenatal screening is a method of assessing pregnancies for birth defects, chromosomal conditions, and genetic disorders that could affect the unborn child. While prenatal care has been around for centuries in one form or another, prenatal screening in comparison, was introduced somewhat recently. ![]() Furthermore, in 77.5% of pregnancies prenatal care was initiated in the first trimester. According to the Centers for Disease Control vital statistics, there were about 3.8 million live births in the United States in 2018.
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