Genetic screening is gaining an increasingly large presence in the world of medical care. The technology is advancing rapidly, providing more and more sophisticated information about an individual’s risk for disorders or disease to the point where a patient might feel overwhelmed. That’s why providers who offer genetic testing also make sure to have staff that is trained to provide counseling to patients about what the results may mean to the health of themselves and their family.
As a woman ages, her risk of having an infant born with a chromosomal disorder such as Trisomy 21 or Down Syndrome increases. It has been a fairly common practice for some time to offer genetic testing to pregnant women who are 35 years or older to determine if their unborn baby has a problem with its genetic make-up. Recently, however, the American Congress of Obstetricians and Gynecologists has recommended that OB/GYN physicians offer testing to all pregnant women who might want to know the risk of their baby being born with one of these conditions.
Just like knowing whether a baby is going to be a girl or a boy, the benefit of knowing if a child is going to be born with Down Syndrome can help the family make preparations in advance should they decide to continue the pregnancy. There are several medical complications that can accompany the delivery of a baby with Down Syndrome and this might affect a patient’s plan to deliver at home versus at a community hospital or larger medical center. There is also long-range planning to take into account, such as physically preparing a home environment that is safe for a baby with special needs. If there are other children at home, there might be a benefit in preparing them mentally and emotionally for a baby with a genetic disorder so that they can provide the care and attention that is necessary for this newborn.
There are three different types of genetic screening tests that are offered at Brattleboro OB/GYN. The first trimester screening test involves having blood drawn and obtaining an ultrasound at some point during the first 10 to 13 weeks of pregnancy. Another type of blood test that can be done during a woman’s second trimester, called a Quad Screen, looks at the levels of four specific substances in the pregnant woman’s blood to help calculate her risk. A third option is called the Integrated Screen where results of the first trimester test and the Quad Screen are combined together to provide a woman with her risk. This particular option offers the greatest level of sensitivity and accuracy. While none of these tests present any physical danger to a woman or her baby, there is the potential for anxiety and emotional conflict that women should keep in mind when they consider getting a test.
Genetic screening does not indicate that the baby has Down Syndrome. It only calculates the likelihood based on what is found in the blood and ultrasound tests, along with other risk factors like a woman’s age. What is considered high or low risk is completely dependent upon the mother’s point of view. Someone who has a 1 in 100 chance of having a baby with Down Syndrome may feel that that percentage is high while another woman with a 1 in 10 chance might feel reassured as there is a 90 percent chance that her baby will be born without this condition. It’s also important to note that the sensitivity of genetic screening ranges anywhere from 80 to 95 percent, depending on the type of test a woman has. In other words, there is always a chance that this screening test will not detect a chromosomal disorder and there is also a 3 to 5 percent chance that the test will show a false positive result.
If a woman wants to definitively know whether her baby has a chromosomal disorder, there are diagnostic tests that can be done. These tests tell a woman if her baby is affected, rather than the screening tests which tell the woman her risk of having a baby affected. Some women may choose to do this after a genetic screening indicates a high risk, and others may bypass the screening step if they want to know the definite answer. Diagnostic tests are also able to detect other types of chromosomal disorders beyond the two disorders (Trisomy 21 and Trisomy 18) that genetic screening focuses on.
There are two tests available for diagnostic testing. Chorionic villus sampling is available in the first trimester while amniocentesis can be performed in the second trimester. These diagnostic tests do come with more risks than genetic screening because of their invasive nature. Both can place a pregnancy at risk for bleeding, infection, premature rupture of membranes, and even loss of the pregnancy. While the chance of any of these circumstances occurring is very low, it is still a risk we counsel a woman about prior to doing diagnostic testing.
A lot of women I talk to about genetic screening and diagnostic testing ask what I would do if I were them. I can’t answer that question because what I would want to know and how I would react based on my value system could be incredibly different than how they would react. The technology exists to give them the information should they want it and we are there to help them make sense of it. But most importantly, they need to have that conversation with their support system to figure out what’s right for them and their pregnancy.
Ellen Garvey, MD is board certified in obstetrics and gynecology. She practices at Brattleboro OB/GYN, a department of Brattleboro Memorial Hospital.