Abstract
Fetal aneuploidy is the leading cause of pregnancy loss. At least 95% of chromosomally abnormal conceptions are lost before term. Over the years, it has become common to offer genetic amniocentesis or chorionic villus sampling to all women who have increased risk of fetal chromosomal abnormalities. However, due to its invasive nature and associated risks, the practice of offering routine invasive testing to all high-risk pregnant women has been challenged. Owing to evolving improvement in high-quality sonographic imaging, it has become apparent that many chromosomal abnormalities that are associated with fetal structural abnormalities or aneuploidy markers are capable of being detected by ultrasound. Since fetuses with trisomies 18 and 13 have many major structural abnormalities, ultrasound has a high sensitivity for detecting them. On the other hand, over the years, investigators have been looking for sonographic markers to increase the detection rate for Down syndrome on prenatal sonography. This has led to the development of the genetic sonogram, which improves the efficiency of prenatal screening for Down syndrome. There has also been a great deal of evidence showing that effective screening for major chromosomal abnormalities can be provided in the first trimester. This is accomplished by examining the nuchal translucency, as well as other important sonographic markers for aneuploidy, combined with maternal serum screening. Screening for chromosomal abnormalities in the first trimester has the distinct advantage of earlier prenatal diagnosis for patients. Therefore, this review will focus on the role of first- and second-trimester ultrasonography as a means of screening for prenatal chromosomal abnormalities and patterns of malformations associated with the most common autosomal trisomies (Down syndrome, trisomy 18 and trisomy 13).
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.