Navigating genetic screening before and during pregnancy
Sequencing the human genome has led to new advances in genetic testing before and during pregnancy. With new, noninvasive technology, women have more choices—and more decisions—regarding their potential offspring and genetic mutations.
Genetic testing became widely available with the completion of the Human Genome Project in the early 2000s. It’s a relatively new technology, says Lee Shulman, MD, medical co-director of Insight Medical Genetics, a cutting-edge genetic testing practice.
As with any new technology, there is a learning curve. That can make genetic testing feel overwhelming for mothers and couples. But fear not. What was once unknown is becoming more commonplace.
Importance of Genetic Counseling
While the protocol for preconception and prenatal genetic testing continues to evolve, most healthcare professionals recommend that patients see a licensed and certified genetic counselor if they are interested in genetic testing. They discourage testing through direct-to-consumer companies, which often don’t explain test results, leaving patients in the lurch if they discover they carry genetic mutations.
“It’s much easier to go into a situation knowing what the possible outcomes are than to find out that something’s potentially wrong and be struggling [afterward] to deal with that information,” says genetic counselor Tabitha Poorvu, MS, CGC, at Insight Medical Genetics.
“My role is to have a conversation with people and explain the different testing options available—ones that are particularly applicable to patients—and then review options with them,” she says.
Risk Versus Diagnosis
A doctor may recommend genetic counseling and testing for several reasons. However, “there’s a difference between screening and diagnostic [testing],” Shulman emphasizes.
Genetic screening identifies whether you’re at an increased risk of giving birth to a child with a genetic disorder like Down syndrome, cystic fibrosis, sickle cell disease or Tay-Sachs disease. The screening cannot determine whether a baby actually will have a disorder.
Before a couple tries to conceive, they can undergo carrier screening, in which a sample of saliva or blood is tested to see whether it carries certain gene mutations. If the mother comes back screen negative, testing might stop there. If she’s screen positive, her partner should be tested, Shulman and Poorvu explain. However, if both parents are carriers for a genetic disorder—usually meaning they have a 25 percent chance of passing on that disorder—they have several options.
A couple can elect in vitro fertilization (IVF) and then screen embryos through a process called preimplantation genetic diagnosis (PGD). With PGD, doctors are able to identify genetic mutations in the embryo. Patients can then implant embryos that do not have the genetic disorder.
Many people choose to wait until they achieve pregnancy and proceed with a screening blood test to determine whether they are a carrier of a gene mutation and to assess the chromosomal status of their fetus.
Cell-free DNA screening, performed during the first trimester of pregnancy, is the newest advance in genetic testing. This noninvasive screening analyzes fetal DNA by sampling the mother’s blood to assess the status of the fetus’s chromosomes. It is mainly used for women at higher risk of chromosomal conditions. Cell-free DNA is a screening test, though, and isnot diagnostic.
For now, chorionic villus sampling (CVS) and amniocentesis are the standard when it comes to prenatal diagnosis. These invasive diagnostic tests analyze the baby’s DNA directly, starting at 10 weeks of pregnancy, for chromosomes as well as for conditions identified in parents who were found to be positive by carrier screening. Though generally safe, invasive prenatal testing can pose a risk to the pregnancy.
Rabbi Aaron Melman of Congregation Beth Shalom in Northbrook and his wife, Elisa, are both carriers of Tay-Sachs disease, which means they have a 25 percent chance of having a child with Tay-Sachs, a disorder in which children lose motor skills and mental functions and usually die by age five.
When they were ready to have children in 2003, their insurance didn’t cover IVF, so they could not do PGD. Instead they tested for Tay-Sachs through CVS during pregnancy. They ended up terminating two pregnancies due to Tay-Sachs, but fulfilled their family dream of two children. Today, they have a healthy son, 11, and daughter, 8.
On making their decision, Rabbi Melman says, “We knew that wasn’t a life we were prepared to bring into this world, to suffer and to watch everyone around that life suffer. … That doesn’t mean there still wasn’t a mourning process. There’s still a sense of loss, and you still think about that life that would have been born.”
But the Melmans have no regrets. “Knowledge is power,” and that includes genetic counseling, he says. “I talk about this with every single couple who I marry.”
Patients who are carriers of a genetic mutation can also consider using a noncarrier egg or sperm donor, or adopting. Depending on the genetic disorder and personal beliefs, some patients choose to accept an affected child and begin planning for that life with a specialist.
“Right now, what we screen for in many ways is a moving target,” says reproductive endocrinologist Jennifer Hirshfeld-Cytron, MD, of Fertility Centers of Illinois, a practice that specializes in fertility and preconception testing, “as the diseases that can be tested for and technologies utilized continue to improve.”
Screening panels vary between physician practices. Previously, patients were screened based on their ethnicity, but screens are now more comprehensive, Hirshfeld-Cytron says. Patients are screened for specific DNA sequences associated with mutations, or the entire genome can be screened.
As scientists continue to decipher the human genome, doctors will be able to test for more genetic disorders. However, most patients who seek genetic testing are low risk.
“After we get past the 10 most common conditions, we are in a sea of very rare problems,” Shulman says. “And in most instances, genetic testing really provides reassurance.”