Screening for Fetal Aneuploidy

Prenatal genetic screening is designed to assess whether a patient is at increased risk of having a fetus affected by a genetic disorder. In contrast, prenatal genetic diagnostic testing is intended to determine, with as much certainty as possible, whether a specific genetic disorder or condition is present in the fetus. The purpose of prenatal screening for aneuploidy is to provide an assessment of the woman's risk of carrying a fetus with one of the more common fetal aneuploidies. This is in contrast to prenatal diagnostic testing for genetic disorders, in which the fetal chromosomes are evaluated for the presence or absence of abnormalities in chromosome number, deletions, and duplications, or the fetal DNA is evaluated for specific genetic disorders. The wide variety of screening test options, each offering varying levels of information and accuracy, has resulted in the need for complex counseling by the health care provider and complex decision making by the patient. No one screening test is superior to other screening tests in all test characteristics. Each test has relative advantages and disadvantages. It is important that obstetrician-gynecologists and other obstetric care providers be prepared to discuss not only the risk of aneuploidy but also the benefits, risks, and limitations of available screening tests. Screening for aneuploidy should be an informed patient choice, with an underlying foundation of shared decision making that fits the patient's clinical circumstances, values, interests, and goals. The purpose of this Practice Bulletin is to provide current information regarding the available screening test options for fetal aneuploidy and to review their benefits, accuracy, and limitations. For information regarding prenatal diagnostic testing for genetic disorders, refer to Practice Bulletin No. 162, Prenatal Diagnostic Testing for Genetic Disorders.