The quadruple screen test is a blood test done during pregnancy to determine whether the baby is at risk for certain birth defects.

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 substances:

• 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:

• Your age
• Your ethnic background
• Your weight
• Your baby’s gestational age

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.

To find out if your baby might be at risk for certain birth defects, such as Down syndrome and neural tube 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.

During pregnancy, increased levels of AFP may be due to a problem with the developing baby, including:

• Spina bifida
• Anencephaly
• Omphalocele
• Tetralogy of Fallot
• Duodenal atresia
• Turner syndrome
• Intrauterine death (usually results in a miscarriage)

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:

• Down syndrome
• Edwards syndrome

An abnormal test result doesn’t mean that your baby definitely has a birth defect. Sometimes results can be abnormal if your baby is older or younger than the health care provider had thought.

If your test results are abnormal, your health care provider may do other tests, including:

• A test that checks the fluid around the baby (amniocentesis)
• Ultrasound to check the baby’s brain, spinal cord, kidneys, and heart

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.

ACOG Committee on Practice Bulletins. ACOG practice bulletin no. 77: screening for fetal chromosomal abnormalities. Obstet Gynecol. 2007;109:217-227.

Graves JC, Miller KE. Maternal serum triple analyte screening in pregnancy. Am Fam Physician. 2002;65:915-920, 922.