Tehran University Medical Journal

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.

Background: For every pregnant woman, it is possible to have a child with chromosomal abnormalities. Although this possibility is not very high, by performing screening tests and considering the mother's background factors, we can largely realize the real extent of this possibility.
Many comorbidities (like high blood pressure, diabetes, and obesity) and high-risk exposures (like alcohol consumption) seem to have an important role in the development of chromosomal abnormalities. This study aimed to determine the predictive factors of a positive first-trimester screening test in the pregnant women.
Methods: This case-control study was done on pregnant women, who were referred to Yas Hospital for their first-trimester screening tests between April 2018 and February 2020. Of those who had positive screening test results, only ones with abnormal biochemical tests, were included in the study regardless of nuchal translucency (NT) examination results and were considered as cases, and the women with normal screening test results were considered as controls.