Triple Screen Test
A triple screen is a prenatal test that measures the mother's blood to help evaluate the heath of the fetus.
Triple screen tests are most accurate when done between the 16th and 18th weeks of pregnancy, though they may be performed as early as 15 weeks or as late as 22 weeks.
The triple screen measures three factors:
- alpha-fetoprotein (AFP)
- human chorionic gonadotropin (HCG)
- unconjugated estriol
Sometimes a fourth factor called inhibin A is also measured. The screening test is called a quadruple test if it also measures inhibin A.
The results of the blood test can help determine if your baby may be at higher risk for certain birth defects.
What does alpha fetoprotein (AFP) measure?
During pregnancy, increased levels of AFP may be due to a problem with the developing baby, including:
- Neural tube defects (NTDs), such as spina bifida or anencephaly
- Duodenal atresia
- Tetralogy of Fallot (TOF)
- Turner syndrome
High AFP can also mean that a woman is pregnant with twins or triplets.
Low levels of AFP and estriol and high levels of hCG and inhibin A may be due to a problem such as Down syndrome (Trisomy 21).
Why is it called a screening test?
These test results can only show that there may be a problem, but they cannot prove that there definitely is one. An abnormal test result doesn't necessarily mean that your baby has a birth defect.
Most often, the blood test results are abnormal because the baby is younger or older than your doctor initially thought. And some birth defects will not be detected by this test. Remember, this test does not screen for all birth defects.
What happens if the test results of the triple screen are abnormal?
If the triple screen tests shows abnormalities, your doctor may recommend repeating the triple or quadruple screen test, or ordering additional tests.
A prenatal ultrasound is often ordered to evaluate the age of the baby and look for problems in the baby's brain, spinal cord, kidneys and heart.
An amniocentesis may also be ordered to check the fluid around the baby.
The results of these tests will help your doctor decide if your baby might have a defect that needs additional evaluation and possible treatment.