gynecology and obstetrics
Preconception or Prenatal Carrier Testing of Parents
Prenatal Testing to Detect Fetal Genetic Abnormalities
 using one of several methods (eg, ell-free DNA serum tests, analyte screening) ( Testing references ). If such a screening test is positive, it may be followed up with include screening for fetal Down Syndrome (Trisomy 21) , Fetal genetic diagnostic testsare usually recommended if risk of a fetal chromosomal abnormality is increased (see table). Fetal genetic diagnostic tests, unlike screening tests, are usually invasive and involve fetal risk. Thus, in the past, these tests were not routinely recommended for women without risk factors or a known genetic abnormality in one of the parents. However, because fetal genetic diagnostic tests are now more widely available and safety has improved, it is recommended to offer fetal genetic testing to all pregnant patients, regardless of risk. Fetal genetic diagnostic tests include Chorionic Villus Sampling , Fetal genetic diagnostic tests can detect all trisomies, many other chromosomal abnormalities, and several hundred mendelian abnormalities. Submicroscopic chromosomal abnormalities are missed by traditional karyotype testing and can be identified only by microarray technologies, such as array comparative genomic hybridization and single nucleotide polymorphism (SNP)-based arrays. Array comparative genomic hybridization in prenatal testing is most frequently used to evaluate fetuses with structural abnormalities. Arrays detect numeric chromosome abnormalities (eg, trisomies) as well as unbalanced structural chromosome disorders, such as microdeletions. Studies have reported about 6% incidence of array abnormalities that would have been missed with traditional karyotyping in structurally abnormal fetuses. Preimplantation Genetic Testing (PGT) may be available for partners who are using 1.American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics; Committee on Genetics; Society for Maternal-Fetal Medicine: Screening for fetal chromosomal abnormalities: ACOG Practice Bulletin, Number 226.Obstet Gynecol. 2020;136(4):e48-e69. doi:10.1097/AOG.0000000000004084 