Prenatal Diagnostic Tests of Genetic Disorders: Review Article



Aryan Z^{1, 2} ; Bahadori A^{1, 3} ; Farhud D^{1, 4}
Source: Tehran University Medical Journal Published:2019

Abstract

The purpose of prenatal diagnosis tests is insisting of diagnosis of neonatal disorders, preparing a range of informed choices and making couples at risk to be ready for having children with genetic disorders as well. The aim of this article is to investigate all of the tests in order to determine the best one which has the lowest risk and the highest sensitivity. Screening tests (maternal blood test and ultrasonography for first and second trimester) are testing patients without symptoms who are at low risk. These tests are carried out in the early stages of pregnancy, and the risk of genetic diseases would be estimated. They are safe and also might be helpful in determining whether invasive prenatal genetic tests including chorionic villus sampling, amniocentesis, and percutaneous umbilical blood sampling are needed. Diagnostic test is insisting of invasive tests: amniocentesis, chorionic villus sampling (CVS), cordocentesis, and preimplantation genetic diagnosis (PGD), which is a genetic test on cells removed from embryos to help select the best ones to avoid some of genetic diseases, fluorescence in situ hybridization (FISH), QF-PCR, multiplex ligation probe amplification (MLPA), next generation sequencing (NGS), comparative genomic hybridization (CGH), and non-invasive tests: ultrasound, prenatal sonography, cell free fetal DNA, triple and quadruple screen: alpha fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), inhibin-A). These tests are intended for patients who have apparent symptoms and the results of their early stages of pregnancy have been positive. Non-invasive prenatal tests (NIPT), sometimes called noninvasive prenatal screening (NIPS), have features of both screening and diagnostic tests, but, now screening test is more considerable. Small fragments of DNA would be analyzed by this testing in which they are circulating in a pregnant woman’s blood. While most DNA is found inside a cell’s nucleus, these fragments are free-floating and not within cells, at this point, they are called cell-free DNA (cfDNA) which usually contain fewer than 200 DNA building blocks (base pairs). Non-invasive prenatal tests is more sensitive with the high degree of specify to determine trisomy 13, 18 and 21 in women who are at increased risk of having offspring with genetic disorders. © 2019, Tehran University of Medical Sciences. All rights reserved.