When you are pregnant, genetic screenings can determine your baby’s risk for certain birth defects. Screenings can show the likelihood that your baby could be born with conditions such as Down syndrome, trisomy 18, spina bifida, or other birth defects.

It is important to note that screenings do not offer a diagnosis. They cannot determine for certain that your baby has a birth defect. They can only tell you whether your baby is at increased risk for some of the most common birth defects. If the risk is high, you may choose to do a diagnostic test. Sometimes diagnostic tests are more invasive, which is why screening is an important first step.

Path to improved health

Most prenatal screening takes place when you are 15-20 weeks pregnant. All pregnant women are offered this screening, but it is optional. You may choose not to do the screening.

If you decide you would like to do the screening, your doctor will order a maternal (from the mom) serum screen (blood test). This could be a “triple screen,” a “quad screen,” or a “penta screen.” The difference between these screens is that they screen for the presence of different proteins in the blood.

There is a newer screening called cell-free DNA screening, which also requires a blood sample from the mom. This screening can be done after 10 weeks of pregnancy.

None of these screenings pose a risk to mom or baby. If you choose to do a screening, you and your doctor can decide which one is best for you.

What is a triple screen?

A triple screen measures three substances in a pregnant woman’s blood: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol.

What is a quad screen?

A quad screen is a blood test that measures four things in a pregnant woman’s blood: AFP, hCG, unconjugated estriol and inhibin A.

What is a penta screen?

A penta screen measures a fifth substance called hyperglycosylated human chorionic gonadotropin.

What is a cell-free DNA screen?

This blood test may be more sensitive than the others. It collects DNA from the baby that is present in the mother’s bloodstream. It uses these DNA fragments to predict the baby’s risk for birth defects.

How do these screenings predict birth defects?

Your doctor uses these blood levels to help predict your baby’s risk for birth defects. But he or she will also look at the mother’s age and other risk factors. For example, if another person in your family has a birth defect, it could mean that your baby is at higher risk for the same birth defect.

What happens if the test results of the screen are abnormal?

Your doctor will probably want you to have an ultrasound. The ultrasound can check on the age of the baby and look for problems in the baby’s brain, spinal cord, kidneys, and heart. Your doctor may want you to talk to a genetic counselor (an expert who can explain the results), get some additional testing, and see a doctor who specializes in high-risk pregnancy.

Things to consider

Screening for birth defects is a personal decision. If your screening is positive (abnormal), would you be willing to do a diagnostic test? Would you handle the pregnancy differently? These are things to consider when making your decision.

Also, keep in mind that the screenings are not absolute. False positives do happen. This could make your pregnancy more stressful, especially if you already know you will not do a diagnostic test. By contrast, a good result could give you peace of mind during your pregnancy.

Questions for your doctor

  • Do you recommend that I have this screening?
  • Am I at a higher risk for having a baby that has a birth defect?
  • What are the next steps if my screening is positive (abnormal)?
  • Can the screening predict all kinds of birth defects?

Resources

Centers for Disease Control and Prevention, Prenatal Testing

Maternal Serum Triple Analyte Screening in Pregnancy by Graves JC, Miller KE (American Family Physician 03/01/02)

National Institutes of Health, MedlinePlus: Prenatal Testing