Prenatal cell-free DNA screening can be used to screen for fetal sex, fetal rhesus (Rh) blood type and the increased chance for specific chromosome problems, including:
- Down syndrome (Trisomy 21)
- Trisomy 18
- Trisomy 13
- Trisomy 16
- Trisomy 22
- Sex chromosome aneuploidy
The conditions included in the screening panel vary based on the lab.
Prenatal cell-free DNA screening is much more sensitive and specific than traditional first and second trimester screening, such as the first trimester screening and the quad screen. As a result, prenatal cell-free DNA screening can often help women who have certain risk factors avoid invasive testing that carries a slight risk of miscarriage, including amniocentesis and chorionic villus sampling (CVS).
Your health care provider might recommend prenatal cell-free DNA screening first if:
- You have risk factors for having a baby who has a chromosomal condition. Risk factors might include older maternal age or having previously given birth to a baby who has Down syndrome, trisomy 13 or trisomy 18. Your health care provider might also recommend prenatal cell-free DNA screening if you've received worrisome results from another prenatal screening test.
- You're a carrier of an X-linked recessive disorder. X-linked recessive disorders, such as Duchenne muscular dystrophy or a blood-clotting disorder (hemophilia), typically affect only males. Prenatal cell-free DNA screening can determine fetal sex earlier than an ultrasound. However, the screening won't determine if the fetus has the disorder. Depending on your test results, a genetic counselor can help you understand the next steps.
- You have an Rh negative blood type. Prenatal cell-free DNA screening can determine the Rh factor of the fetus. If you're Rh negative and the fetus is Rh positive, you might produce Rh antibodies after exposure to fetal red blood cells. This is typically not a concern during a first pregnancy, but can be a concern during subsequent pregnancies.
Still, prenatal cell-free DNA screening has limits. Data suggests that when this screening is used by the general obstetric population, rather than by women who have specific risk factors, there will be more false-positive test results. The American College of Obstetricians and Gynecologists considers traditional screening methods the most appropriate choice for first line screening for most women in the general obstetric population.
In addition, prenatal cell-free DNA screening has been shown to be less effective if you are:
- Pregnant with multiples
- Pregnant via a donor egg
- Pregnant and a surrogate
- Less than 10 weeks pregnant