Screening For Genetic Disorders
GENETIC SCREENINGS VS. TESTS
NIPT is a prenatal screening, which looks at DNA from your baby’s placenta in a sample of your blood to identify whether you’re at increased risk of giving birth to a child with a genetic disorder. A screening like NIPT cannot, however, determine for sure whether your baby actually has a chromosomal disorder, only the likelihood of having that condition. But even though it can’t tell for sure whether your baby has a genetic abnormality, it is highly accurate — 97 to 99 percent accuracy for three of the most common conditions, according to a recent study.
The results of an NIPT screening can help you and your doctor decide next steps, including whether to have a diagnostic test like chorionic villus sampling (CVS) or amniocentesis (“amnio”). These genetic tests analyze a baby’s own genetic material, collected from the amniotic fluid or placenta, to tell with 100 percent certainty whether a baby has a chromosome abnormality. However they are invasive, which means they slightly increase the chance of miscarriage.
WHAT NIPT SCREENS FOR
All NIPTs screen for the most common chromosomal disorders:
- Trisomy 21 (Down syndrome)
- Trisomy 18 (Edwards syndrome)
- Trisomy 13 (Patau syndrome)
WHAT ARE THE DIFFERENT KINDS OF NIPTS?
Four companies currently offer noninvasive prenatal testing: Genesis Serenity, Harmony, Natera and MaterniT21. Each company offers slightly different panels screening for various genetic disorders. Some screen for abnormalities including triploidy and microdeletion. It’s worth noting that while some brands differentiate between maternal and fetal cfDNA, others do not (which means they’re less accurate), so you might want to ask your practitioner which type of test she uses.
WHEN IT’S DONE
NIPT can be performed any time after 10 weeks into your pregnancy — earlier than any other prenatal screening or diagnostic test. In comparison, nuchal translucency screening is done between weeks 11 and 13; CVS is done at 10 to 13 weeks; the quad screen is completed between weeks 14 and 22; and amniocentesis is usually performed between weeks 16 and 18, though it’s sometimes done as early as week 13 or 14 and as late as week 23 or 24.
THE ACCURACY OF NIPT
Research suggests that NIPTs create fewer false alarms than standard first-trimester blood screenings (like first-trimester bloodwork or quad screening) that measure hormones and special proteins in Mom’s blood. Other research has shown that NIPTs are more accurate than those same standard screenings in predicting the risk of Down syndrome (NIPTs are 99 percent accurate) and Edwards syndrome. The American Congress of Obstetricians and Gynecologists (ACOG) says NIPT needs to be further evaluated before it will recommend the screening for all pregnant women.
Other tests, procedures, and referrals that may be needed include the following:
- High level fetal ultrasounds: A detailed ultrasound of the rest of the fetus is necessary to follow fetal growth, monitor fetal well-being, and assess the rest of the fetus for abnormalities in other organs.
- Fetal MRI: This test is becoming more widely available and can provide additional information about the overall health of the fetus and problems with certain organs.
- Genetic counseling: Geneticists and genetic counselors provide an assessment of the likelihood of a genetic syndrome and possible abnormalities in other organs based on the heart diagnosis and other findings in the fetus. The geneticist can provide information to patients and their relatives concerning the consequences of a disorder, the probability of developing or transmitting it, and ways in which it can be prevented, treated, and managed.
- Perinatologist: Perinatologists can advise you about the management of your pregnancy, options for deciding whether on not to continue the pregnancy, and planning for delivery
- Social worker/Nurse: Someone who is familiar with heart disease in children, can provide information about caring for a child with congenital heart disease.
- Amniocentesis: This is a test performed to determine chromosomal and genetic disorders and certain birth defects. The test involves inserting a needle through the abdominal and uterine wall into the amniotic sac to retrieve a sample of amniotic fluid.
- Specialist consultation: Depending on the diagnoses you may be referred to other subspecialists including general surgeons, neurosurgeons, orthopedic surgeons, and urologists.