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Ease your pregnancy anxiety with prenatal testing


Diana Charkalis for GBMC

January 9, 2018
When prenatal genetic counselor Amy Kimball meets with an expectant mom, she spends up to 45 minutes learning about the family, while discussing options for detecting whether the baby is at risk for a genetic condition like Down syndrome or a birth defect.

Often, Kimball says, the patient has been referred to her office at the Harvey Institute for Human Genetics at Greater Baltimore Medical Center by her obstetrician. And she may have questions.

“There’s not usually a lot of time to discuss the pros and cons of genetic testing at the obstetrician’s office,” Kimball says. “There’s so much else to do at every appointment. I really try to approach families individually because everyone comes into this from a different place with a different history, different values and different levels of worry.”

Who should be tested?

Although any woman can get prenatal genetic counseling at the Harvey Institute, women 35 and older are most commonly seen, Kimball says. And women of all ages are coming in with questions about newer noninvasive genetic screening tests.

Counselors help families decide which tests make sense for them. “Now laboratories offer screening for hundreds of genetic conditions,” says Natalie Blagowidow, M.D., director of the Prenatal Diagnostic Center at the Harvey Institute. The Institute helps expectant parents sort through how much they really want to know and how many of these conditions they are truly interested in being screened for. Some couples might just want to do an ultrasound looking for birth defects without homing in on genetic abnormalities. Other couples want to know everything possible.

A new option in noninvasive screening

During the first trimester, two noninvasive screenings are available at GBMC. The first is an ultrasound at 11 to 13 weeks. It can identify markers that may indicate the possibility 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, which Blagowidow says is now considered the best noninvasive screening tool for detecting Down syndrome prenatally. “Many women are now electing to do this newer blood test that looks at the DNA from the baby that’s in the mother’s blood,” says Blagowidow. Benefits of the test include a less than 1 percent false positive rate for Down syndrome and no increased risk of miscarriage. The test also provides a high detection rate for abnormalities such as trisomy 18 and certain sex chromosome abnormalities. “Currently it’s being offered to anyone with an interest in having it, and many insurance companies cover the test now,” Blagowidow says.

Predicting the baby’s sex

The test also predicts fetal sex. Patients of all ages come in requesting “the test that tells the sex of the baby,” Kimball says. She explains that the main purpose of the test is to detect genetic issues so that patients can make well-informed decisions and can have the opportunity to prepare for life after delivery.

“We really need to think about this from the clinical standpoint. It’s great to learn the sex, but you could also hear bad news. So is it worth it? Thankfully, the vast majority of the time we get to give reassuring results. But not always.”

Diagnostic testing risks and benefits

Diagnostic tests include chorionic villus sampling, or CVS, and amniocentesis. They are more invasive, but can detect certain disorders with the most certainty, according to the American Congress of Obstetricians and Gynecologists. CVS can be performed between 10 and 12 weeks of pregnancy. A small sample of tissue is obtained from the placenta and used to analyze the chromosomes. This is done by inserting a small catheter through the cervix or by inserting a needle through the abdomen. Amniocentesis can be performed between 16 and 18 weeks, and is used to detect chromosome conditions such as Down syndrome. During amniocentesis, a thin needle is inserted into the amniotic sac to withdraw a small amount of fluid. Both amniocentesis and CVS carry a small risk for miscarriage.

Studying anatomy at 18 weeks

An ultrasound performed between 18 and 20 weeks is recommended for all pregnancies to check the baby’s anatomy. This ultrasound can detect many, but not all, birth defects. It may also identify markers that might indicate a specific chromosome abnormality, such as Down syndrome, in the pregnancy. During the ultrasound, the doctor looks head to toe at fetal anatomy, making sure that everything they can see has formed correctly. As technology continues to advance, the field of prenatal testing gets more complicated, but also more rewarding, Kimball says. “With every new screening, we’ve gotten better at what we’re doing. It keeps us on our toes. It certainly hasn’t gotten boring. It’s really challenging in a good way.”
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