This test is usually performed between the 15th and 22nd weeks of the pregnancy, but it is most accurate between the 16th and 18th weeks.
Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
The blood sample is sent to a laboratory for testing.
The test measures levels of four pregnancy hormones:
- Alpha-fetoprotein (AFP) – a protein produced by the baby
- Human chorionic gonadotropin (hCG) – a hormone produced in the placenta
- Unconjugated estriol (uE3) – a form of the hormone estrogen produced in the fetus and the placenta
- Inhibin A -- a hormone released by the placenta
If the test does not measure levels of inhibin A, it is called the triple screen test.
To determine the chance of your baby having a birth defect, the test also factors in:
No special preparation is necessary.
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
The test is done to find out if your baby might be at risk for certain birth defects, such as Down syndrome and birth defects of the spinal column and brain (called neural tube defects).
All pregnant women should be offered this test. The quadruple screen test is normally done some time between the 15th and 20th week of pregnancy.
Certain women are at greater risk for having a baby with these defects. These women include those over 35 years old during pregnancy, those taking insulin to treat diabetes, and those with a family history of birth defects.
This test is a screening test. This means it does not diagnose birth defects. Instead, it indicates whether your baby has a higher risk of these defects.
Normal levels of AFP, hCG, uE3, and inhibin A.
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
An abnormal test result does NOT mean that your baby definitely has a birth defect. Often, the results can be abnormal if your baby is older or younger than the health care provider had thought. Common next steps by your doctor may include:
- Performing an ultrasound, which will help identify the exact age of the fetus and will also be able to closely examine the skull, spine, and other organs of the fetus
- Repeating the test
If abnormal results are still present, further testing and counseling can be done. Some individuals or couples choose not to have any more tests done, for personal or religious reasons. Possible next steps include:
Amniocentesis,which checks the AFP level in the amniotic fluid surrounding the fetus, and also looks at the fetal cells (specifically the fetal chromosomes) to detect or rule out certain birth defects (such as Down syndrome)
- Genetic counseling
- Ultrasound to check the baby’s brain, spinal cord, kidneys, and heart
During pregnancy, increased levels of AFP may be due to a problem with the developing baby, including:
High AFP can also mean that you’re carrying more than one baby.
Low levels of AFP and estriol and high levels of hCG and inhibin A may be due to a problem such as:
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
The quadruple screen can have false-negative and false-positive results (although it is slightly more accurate than the triple screen). Additional tests are needed to confirm the results.
If the test is abnormal, you may want to talk to a genetic counselor.