Washington, DC -- All pregnant women, regardless of their age, should be offered screening for Down syndrome, according to a new Practice Bulletin issued today by The American College of Obstetricians and Gynecologists (ACOG). Previously, women were automatically offered genetic counseling and diagnostic testing for Down syndrome by amniocentesis or chorionic villus sampling (CVS) if they were 35 years and older.
The new ACOG guidelines recommend that all pregnant women consider less invasive screening options for assessing their risk for Down syndrome, a common disorder that is caused by an extra chromosome and can result in congenital heart defects and mental retardation. Screening for Down syndrome should occur before the 20th week of pregnancy.
"This new recommendation says that the maternal age of 35 should no longer be used by itself as a cut-off to determine who is offered screening versus who is offered invasive diagnostic testing," noted Deborah Driscoll, MD, a lead author of the document and vice chair of ACOG's Committee on Practice Bulletins-Obstetrics, which developed the Practice Bulletin with ACOG's Committee on Genetics and the Society for Maternal-Fetal Medicine.
ACOG also advises that all pregnant women, regardless of their age, should have the option of diagnostic testing. ACOG recognizes that a woman's decision to have an amniocentesis or CVS is based on many factors, such as a family or personal history of birth defects, the risk that the fetus will have a chromosome abnormality or an inherited condition, and the risk of pregnancy loss from an invasive procedure.
According to the new guidelines, the goal is to offer screening tests with high detection rates and low false positive rates that also provide patients with diagnostic testing options if the screening test indicates that the patient is at an increased risk for having a child with Down syndrome. Because of the number of multiple screening strategies currently available, the document provides ob-gyns with some suggested screening strategies that they can choose to offer in their practice to best meet the needs of their patients. The guidelines discuss the advantages and disadvantages of each screening test and some of the factors that determine which screening test should be offered, including gestational age at first prenatal visit, number of fetuses, previous obstetrical and family history, and availability of various screening tests.
The following ACOG recommendations are based on good and consistent scientific evidence:
- First-trimester screening using both nuchal translucency (NT), an ultrasound exam that measures the thickness at the back of the neck of the fetus, and a blood test is an effective screening test in the general population and is more effective than NT alone.
- Women found to be at increased risk of having a baby with Down syndrome with first-trimester screening should be offered genetic counseling and the option of CVS or mid-trimester amniocentesis.
- Specific training, standardization, use of appropriate ultrasound equipment, and ongoing quality assessment are important to achieve optimal NT measurement for Down syndrome risk assessment, and this procedure should be limited to centers and individuals meeting this criteria.
- Neural tube defect screening should be offered in the mid-trimester to women who elect only first-trimester screening for Down syndrome.
Practice Bulletin #77, "Screening for Fetal Chromosomal Abnormalities," is published in the January 2007 issue of Obstetrics & Gynecology.