The American College of Obstetricians and Gynecologists (ACOG) recently expanded its guidelines on carrier screening for genetic disorders with two Committee Opinions that were published in the March 2017 issue of Obstetrics and Gynecology.
Genetic carriers are people who have one copy of a defective gene but typically have no signs or symptoms. Carrier screening is blood and/or saliva testing that lets prospective parents know whether they each are carriers and are at risk of passing on two defective gene copies, one from each them, to any children who then would be affected by the disease.
Previously, ACOG recommended that carrier screening be offered to patients based largely on their ethnic background and family history. The new guidance broadens the recommendations for who should be screened and for which disorders. Generally, carrier screening should be discussed with all pregnant women as well as those considering pregnancy.
Among specific recommendations are that all pregnant women or those considering pregnancy should receive information regarding carrier screening for cystic fibrosis, spinal muscular atrophy (SMA), and Fragile X syndrome. Other conditions such as hemoglobinopathies (thalassemia and sickle cell disease) are also candidates for carrier screening. A complete blood count is recommended to accompany screening for these inherited blood diseases since anemia may be an indication of these diseases.
"Genetic conditions…are not limited to one ethnic group. And certain conditions are common enough that it's essential [to] offer screening for them in every patient," says Joseph R. Biggio Jr., MD, chair of the ACOG Committee on Genetics and Associate System Chair for Women's Services for the Ochsner Health System in New Orleans. "A growing number of Americans are also of mixed or uncertain ethnic backgrounds," says Dr. Biggio, "which means we may not identify some people who are at risk of passing genetic conditions to their children when we follow ethnic-based recommendations."
Beyond the specific recommendations, the new guidelines advise that healthcare practitioners and practices establish their own standards for offering carrier screening. While strategies that offer screening based on specific ethnic group are acceptable, healthcare practitioners may offer expanded carrier screening, regardless of ethnic background.
"The specific point about expanded carrier screening means that instead of just offering screening for a select group of disorders, doctors can…use one of the multidisease panels offered by a number of commercial laboratories to offer carrier screening for more than 100 conditions," says Dr. Biggio, who adds that recent technology allows the testing to be done relatively inexpensively.
However, the committee opinion doesn't mean that every condition can or should be screened for. The new opinion says that conditions included in an expanded carrier screening panel should:
- Have a carrier rate of one in a hundred or greater
- Be easily detected by genetic testing
- Have a detrimental effect on quality of life, cause cognitive or physical impairment, require surgical or medical intervention, and begin early in life
The new opinion also says that conditions screened should be able to be detected while the mother is pregnant and have the potential for intervention during pregnancy to possibly improve outcomes, how the delivery is managed, and/or educate parents about any special care needs after birth.
Ideally, carrier screening should be offered to women when they are considering pregnancy but can also be offered during pregnancy. If a woman is found to be a carrier for a genetic disorder, testing should be offered to her partner. Genetic counseling and education should be provided so that patients understand test results, implications of the results, and their risk of passing genetic disorders to any children. This comprehensive process allows the patient to make informed decisions about their own health and potential reproductive options.
"Every obstetrician-gynecologist or other health care provider should establish a standard approach to carrier screening that's consistently discussed with each patient and considers a patient's family history and personal values," according to the committee opinion. "[And]…after counseling, patients can opt to decline any or all carrier screening."