Physicians Natalie Blagowidow, MD, and Shama Jari, MD, work closely with a staff of genetic counselors to help guide patients through the process of prenatal testing in the Center. Patients who might consider such testing include women of advanced maternal age (those who will be 35 or older when they give birth), women with high-risk pregnancies, women with a history of fetal abnormalities in prior pregnancies and women with family histories of genetic conditions. Patients are referred by their obstetricians for prenatal testing. Couples interested in preconception counseling may be referred by their physician or can make appointments themselves.
There are two options for non-invasive screening a pregnant woman can obtain during the first trimester. The first is a detailed fetal ultrasound performed between 11-13 weeks of pregnancy. The ultrasound can identify markers that may indicate a higher chance of the presence of trisomy 13, also known as Patau syndrome, trisomy 18, also known as Edwards syndrome, and trisomy 21, Down syndrome — all of which can lead to major health complications for the mother and fetus. This ultrasound can be combined with bloodwork to determine a risk estimate for chromosomal abnormalities.
The second option is a cell-free fetal DNA screening. “The screening is performed by taking a blood sample from the mother,” says Dr. Blagowidow. The test also provides a high detection rate for abnormalities such as trisomy 18 and certain sex chromosome abnormalities. “The test is currently considered the best non-invasive tool for detecting Down syndrome prenatally,” Dr. Blagowidow adds. She recommends that women who choose the fetal DNA screening also have the detailed first trimester ultrasound.
While the benefits of the blood test are significant — a less than one percent false positive rate for Down syndrome and no increased risk of miscarriage — there are facts to consider before undergoing the screening. “It’s important for patients to know that cell-free fetal DNA testing is not ‘diagnostic,’ like an amniocentesis or chorionic villus sampling,” says Dr. Blagowidow, referring to definitive genetic tests. Cost can also be a drawback, as insurance companies have varying levels of coverage for this new genetic screening.
If a patient undergoes the prenatal screening and the results are positive, genetic counselors will help to facilitate next steps and review the pros and cons of further testing with the patient. “Our goal is to give parents-to-be as much information as possible, while preserving the health of both mother and fetus,” says Dr. Blagowidow.
For additional information about the services offered by the Prenatal Diagnostic Center at the Harvey Institute for Human Genetics at GBMC, visit www.gbmc.org/prenatalgenetics or call 443-849-GBMC (4262).