Results

The quad screen measures levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG), estriol and inhibin A in pregnant women's blood. Your health care provider will use your age at the estimated time of delivery and the results of the quad screen to evaluate your chance of carrying a baby who has certain chromosomal conditions, neural tube defects or abdominal wall defects.

Quad screen results give the level of risk of carrying a baby who has certain conditions compared with the general population's risk. Keep in mind that a positive quad screen simply means that levels of some or all of the substances measured in your blood were outside the normal range. Factors that can affect the substances measured by a quad screen include:

• A miscalculation of how long you've been pregnant
• Maternal race
• Maternal weight
• Carrying more than one baby during a pregnancy
• Diabetes
• In vitro fertilization
• Smoking during pregnancy

If your test results are positive, your health care provider might recommend an ultrasound to verify the baby's gestational age and confirm the number of babies you're carrying.

The quad screen correctly identifies about 80 percent of women who are carrying a baby who has Down syndrome. About 5 percent of women have a false-positive result, meaning that the test result is positive but the baby doesn't actually have Down syndrome.

When you consider your test results, remember that the quad screen only indicates your overall chance of carrying a baby who has certain chromosomal conditions, neural tube defects or abdominal wall defects. A decreased chance (negative screen result) doesn't guarantee that your baby won't have one of these conditions. Likewise, an increased chance (positive screen result) doesn't guarantee that your baby will be born with one of these conditions.

Often, positive screen results might cause you to consider other testing, such as:

• Prenatal cell-free DNA screening. This sophisticated blood test examines cell-free DNA from the placenta and the fetus in the mother's bloodstream. It evaluates whether your baby is at risk of Down syndrome, extra sequences of chromosome 13 (trisomy 13), extra sequences of chromosome 18 (trisomy 18) or a sex chromosome abnormality, such as Turner syndrome. A normal result might eliminate the need for an invasive prenatal diagnostic test.
• Targeted ultrasound. If you're at high risk of a neural tube defect, your health care provider might suggest this test. Ultrasound isn't an effective screening tool for Down syndrome.
• Chorionic villus sampling (CVS). This procedure can be used to diagnose chromosomal conditions, such as Down syndrome. During CVS, a sample of tissue from the placenta is removed for testing. CVS poses a slight risk of miscarriage and isn't useful in detecting neural tube defects, such as spina bifida.
• Amniocentesis. Amniocentesis can be used to diagnose both chromosomal conditions and neural tube defects. During amniocentesis, a sample of amniotic fluid is removed from the uterus for testing. Like CVS, amniocentesis poses a slight risk of miscarriage.

Your health care provider or a genetic counselor will help you understand your test results and what the results might mean for your pregnancy.