The subject arises in the early days of pregnancy, when excitement and expectation are interrupted by bouts of morning sickness and fatigue. At about 10 weeks, a mom-to-be will be faced with the prospect of genetic testing, which brings a swirl of emotion all its own.
In recent decades, the offering of prenatal genetic screening has become a routine part of pregnancy, with the subject usually first brought up by an obstetrician during an office visit between eight and 10 weeks. Initially, it’s a simple test — just a blood draw. But the results can be complicated for parents of babies who test positive for a genetic disorder.
In all cases, the screenings are voluntary. “There's no right or wrong answer, because it's very personalized, obviously. Some people want to know this information, and they want to plan ahead. And other people say, ‘I'd rather not,’ because it may introduce more anxiety,” says Spencer Wood, a certified genetic counselor at Summerville Medical Center’s Maternal Fetal Medicine Clinic.
“So, some people just want to take it as it comes, and so they don't want testing. That is absolutely fine with us. We're happy to support whatever women choose to do.”
There are two types of chromosomal screenings available: noninvasive prenatal testing (NIPT), which analyzes DNA in the pregnant woman’s blood, and a first trimester screen, which pairs bloodwork with an ultrasound that measures the space behind the baby’s neck, which can be an indicator of a chromosomal condition. Both are considered noninvasive in that they pose no risk to the baby.
NIPT assesses risk for conditions such as Down syndrome, and trisomy 18 and trisomy 13 — the latter two being abnormalities stemming from extra chromosomes in cell nuclei — while the first trimester screen assesses risk for Down syndrome or trisomy 18. The screenings also reveal the baby’s gender.
NIPT is a newer and more accurate test, Wood says. “A lot of women these days are choosing NIPT because it's more accurate, and the cost has come down substantially,” he adds. “It is a better test. But the guidelines right now essentially say to offer both to patients, and let them decide.”
While NITP is highly accurate — up to 99 percent depending on the abnormality, according to a 2018 study conducted in the United Kingdom — it’s not definitive. Results are confirmed through more-invasive diagnostic tests such as amniocentesis (which draws amniotic fluid) or chorionic villus sampling (which takes tissue from the placenta).
The difference between the two diagnostic tests is the timing: chorionic villus sampling is usually done between 10 and 13 weeks, Wood says, while amniocentesis can be performed as early as 15 weeks. Both procedures carry a slight risk of miscarriage, between .1 to .3 percent for amniocentesis and .22 percent for chorionic villus sampling, according to the Mayo Clinic.
Another type of genetic testing is carrier screening, which determines whether a person carries the gene for certain genetic disorders that can potentially be passed on to the child. According to the American College of Obstetricians and Gynecologists, if both parents are carriers of a recessive gene for a disorder, there is a 25 percent chance that their child will get the gene from each parent and will have the disorder. There is also a 50 percent chance the child will be a carrier of the disorder, as the parents are.
Risks can vary with ancestry. “In general, everybody regardless of ancestry, gets offered carrier screening for cystic fibrosis and spinal muscular atrophy,” Wood says. “If you're African American, you also get offered testing for sickle cell disease, which is by far one of the most common inherited syndromes in the world. It's very common and very serious. Kids who have sickle cell disease, they need serious medical attention. And that's also one of the reasons that disorder is on newborn screening.”
Carrier screening can specifically target disorders based on family history or ethnicity, such as Tay–Sachs disease, a fatal nervous system disorder which is more common in those of Eastern European of French-Canadian decent. Though that approach can be complicated by inaccurate knowledge of ancestry, according to the American Journal of Managed Care.
Expanded screenings are done without regard to family history or ethnicity. The testing involves taking samples of blood, saliva or tissue from the inside of the cheek. Some people choose to undergo carrier screening before becoming pregnant, allowing them to consider an option such as in vitro fertilization with donor eggs or sperm in the case of a positive result.
Although every lab is different, chromosomal testing such as the NIPT typically costs between $200 and $300, Wood says. Carrier screening costs about the same, he adds, and insurance often covers all or most of the cost because both tests are now considered routine elements of prenatal care.
“The labs have actually done a pretty good job of making this stuff affordable to people. Nobody, including doctors and genetic counselors, wants cost to be a barrier to testing that people are interested in. If a patient wants the test, we help them get it at an affordable price, and there is financial aid available through the labs,” Wood says.
“From an ethical standpoint, we don't want to create a situation of, ‘Well, only rich people can get the best testing.’ That's the opposite of what we want. From an ethical standpoint, if a woman comes in and says, ‘I want an NIPT and carrier screening,’ everybody’s on board with that. We make it happen, and help them get it as cheaply as possible.”
Choosing to undergo genetic testing is a personal decision. Obstetricians may refer patients to counselors like Wood to explain the process and answer any questions before the testing occurs. Some parents-to-be want the testing so they’ll know of any abnormalities beforehand, in order to have as much time as possible to make decisions or prepare for the arrival of a child who may have complicated medical issues or special needs.
But a positive result in a prenatal genetic test can also lead to difficult or heart-wrenching moments. Very serious conditions such as trisomy disorders carry short life expectancies that may require the planning of hospice care for the newborn. In some circumstances, parents may decide to end the pregnancy. Religious customs and personal beliefs may play a role in how parents decide to proceed.
Such potential difficulties haven’t slowed the growing popularity of tests like the NIPT, which was used by up to 6 million pregnant women as of late 2017, according to the New England Journal of Medicine. And yet, the ease of the test — or simply the desire to learn the gender of the baby — may blind some to the potential harsh realities.
“In consenting to a blood test that poses no fetal risk, some women may not be fully aware of the limitations of the test or they may give inadequate consideration to the effect of potentially receiving a positive result,” Dr. Diana W. Bianchi of the National Human Genome Research Institute wrote in the Journal.
When advising parents in the wake of a positive test, counselors such as Wood take a “nondirective” approach: They offer information and answer questions, but the patients are the ones in control and are ultimately making any decisions.
“No one is in their shoes except for them,” he says. “So they have to make the decision that is the best for them. We can help them. We can facilitate the decision-making. But we remain nondirective. So it's noncoercive, nonjudgmental, nonbiased. We see ourselves as going every step of the way, side by side with the patient. We're on the same team. We want to be with the patients, and we support the decisions they make.”
Prenatal genetic testing has evolved over time, from the serum screening for Down syndrome pioneered in the 1980s to the NIPT test developed in 2011. Each advancement has allowed doctors and patients to learn more about potential disorders earlier in the pregnancy, often inflaming ethical debates at the same time.
Between genetics counselors and parents-to-be, though, there is no judgment, only support in a potentially difficult time.
“Sometimes we're delivering news that is unexpected and difficult. People like myself want to be there in those moments. We signed up for it. As genetic counselors, we want to be there to help patients in a difficult time. And we take the time. We sit down with patients and really walk through it with them,” Wood says.
“So, these difficult, anxious, hard, unexpected findings or whatever's going on with them in their pregnancy, genetic counselors want to jump right in and be an advocate and help the patient. That's where we want to be, in these high-anxiety situations, in these conversations that can be difficult, so that way the patient can make the best decisions for them and their family.”