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Who should get genetic testing before or during pregnancy?

06/06/2018

Dallas Reed, MD is a medical geneticist at Tufts Medical Center in Boston.If you’re thinking about having a baby, you may be paying more attention to your health: making sure you’re eating nutritious foods, getting enough sleep, exercising, cutting back on alcohol and stopping smoking. And you may be wondering if genetic testing is something you should consider. Dallas Reed, MD, Medical geneticist at Tufts Medical Center recommends starting with a visit to your OB/GYN and sometimes an expert in genetics.

Making an appointment

“There are many reasons to make a preconception appointment. We want to make sure that any medical problems you may have are under control and we want to make sure you’re not on any medications that can cause a problem with the pregnancy,” said Reed. "We also want to talk about genetic testing options.”

For certain genetic conditions, individuals can have a genetic mutation without having any symptoms of the disease. That makes them a carrier for the condition. The American College of Obstetrics and Gynecology (ACOG) recommends that all women be offered carrier screening; if testing shows that a woman is a carrier, her partner should be tested as well. When both parents are carriers for the same condition, they have a 25% risk of having a child with that condition.

ACOG recommends screening for three conditions - cystic fibrosis, spinal muscular atrophy and blood disorders like sickle cell anemia and thalassemias. People of certain ethnic groups, such as Ashkenazi Jews, should also be offered carrier screening for other genetic conditions, including Tay-Sachs disease.

“At that first appointment, we also discuss if there is a family history of any genetic conditions, birth defects, intellectual disability or autism,” said Reed. “This helps us determine if additional genetic testing is recommended.”

When should I have testing done? 

While it’s ideal to get this testing done before becoming pregnant, most women make their first OB/GYN appointment after they’re already pregnant - and that’s okay. The carrier screening and family history discussions are still advised. 

“If you are at risk for passing on one of these conditions to your child, we talk about it,” said Reed. “If that’s something that’s important to you, and it may change the course of your pregnancy, we need to know that sooner rather than later.”

A revolution in high-risk screening

With more couples waiting until their 30s to start their families, Reed has seen an increase in the number of women requesting a specific genetic test to screen for abnormalities at the beginning of pregnancy – the non-invasive cell-free DNA test.

“The cell-free DNA test has revolutionized the screening process,” said Reed. “It’s recommended for people who are high risk - over the age of 35 - or if there’s a previous pregnancy with Down syndrome.”

Before the cell-free DNA test became readily available, the primary doctor-recommended options included amniocentesis or chorionic villus sampling (CVS) to screen for Down syndrome. These tests involve using a needle to obtain a sample of DNA from the placenta, or from the fluid around the baby, and come with a small risk for miscarriage. 

“The cell-free DNA test is a noninvasive blood test. It looks at DNA fragments from the mom and from the placenta, which is a proxy for the fetus,” said Dr. Reed. “It’s a very sensitive test, so if it comes back low risk or normal, and the ultrasound and other tests are normal, we feel very reassured that we don’t have to go to one of the more invasive tests.”

But, she cautions, the test is not diagnostic. 

“I want to emphasize that if the cell-free DNA test comes back abnormal, we strongly, strongly recommend a follow up test with a CVS or amniocentesis,” she said. “That’s the only way to confirm.”

Feeling overwhelmed? You’re not alone. 

“When there’s a family history of a genetic condition, or if any of the genetic tests comes back with an abnormality or an unclear result, the patient should definitely be seen by a genetic counselor,” said Reed. “The counselor can examine and explain family history and risk, and ensure that you get the appropriate screening tests if you want them.”

Some couples want to know everything they can about the pregnancy, while others decline further testing because they know it’s not going to change the management of the pregnancy. 

“Counseling helps put genetics into perspective so you can understand if it’s something you think would matter to you,” said Reed. “The counselor is there to give you your options and help you to think them through based on your own values and feelings.”

It’s important to remember that even if both partners are not carriers, there is still a small risk of a child being affected with a genetic condition.

“The risk is very much reduced, but nothing in genetics is zero,” she said. “It’s important to keep that in mind.”