This test measures the amount of certain substances in the blood of a pregnant woman, who is at risk of having a baby with a birth defect. These substances are alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol, which are proteins and hormones produced by the unborn baby and the placenta (organ that nourishes the baby during pregnancy). This test is used to screen for birth defects in the unborn baby such as Down syndrome, Edward syndrome, or a neural tube defect.
Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:
When and how often laboratory tests are done may depend on many factors. The timing of laboratory tests may rely on the results or completion of other tests, procedures, or treatments. Lab tests may be performed immediately in an emergency, or tests may be delayed as a condition is treated or monitored. A test may be suggested or become necessary when certain signs or symptoms appear.
Due to changes in the way your body naturally functions through the course of a day, lab tests may need to be performed at a certain time of day. If you have prepared for a test by changing your food or fluid intake, lab tests may be timed in accordance with those changes. Timing of tests may be based on increased and decreased levels of medications, drugs or other substances in the body.
The age or gender of the person being tested may affect when and how often a lab test is required. Chronic or progressive conditions may need ongoing monitoring through the use of lab tests. Conditions that worsen and improve may also need frequent monitoring. Certain tests may be repeated to obtain a series of results, or tests may need to be repeated to confirm or disprove results. Timing and frequency of lab tests may vary if they are performed for professional or legal reasons.
The recommended time to do this test is during the 4th month (16 to 18 weeks) of pregnancy.
Before having blood collected, tell the person drawing your blood if you are allergic to latex. Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. Also tell the healthcare worker if you have felt nauseated, lightheaded, or have fainted while having blood drawn in the past.
This test requires written consent. Review the consent form with the healthcare worker and ask any questions that you have before signing the consent form.
When a blood sample from a vein is needed, a vein in your arm is usually selected. A tourniquet (large rubber strap) may be secured above the vein. The skin over the vein will be cleaned, and a needle will be inserted. You will be asked to hold very still while your blood is collected. Blood will be collected into one or more tubes, and the tourniquet will be removed. When enough blood has been collected, the healthcare worker will take the needle out.
The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.
During a blood draw, you may feel mild discomfort at the location where the blood sample is being collected.
After a blood sample is collected from your vein, a bandage, cotton ball, or gauze may be placed on the area where the needle was inserted. You may be asked to apply pressure to the area. Avoid strenuous exercise immediately after your blood draw. Contact your healthcare worker if you feel pain or see redness, swelling, or discharge from the puncture site.
Blood: During a blood draw, a hematoma (blood-filled bump under the skin) or slight bleeding from the puncture site may occur. After a blood draw, a bruise or infection may occur at the puncture site. The person doing this test may need to perform it more than once. Talk to your healthcare worker if you have any concerns about the risks of this test.
Laboratory test results may vary depending on your age, gender, health history, the method used for the test, and many other factors. If your results are different from the results suggested below, this may not mean that you have a disease. Contact your healthcare worker if you have any questions. The following are considered to be normal results for this test:
Laboratory results are evaluated in the context of patient-specific risk taking into account factors such as gestational age, family history, and maternal race, weight, and age. In reporting the results, the laboratory should include the pregnancy and demographic information utilized in the interpretation of the results. Analytic results should be reported in both mass units and interpretive units (multiples of the median), and should include the risk cutoff level used and the patient-specific risk . .
Ask your healthcare worker how you will be informed of the test results. You may be asked to call for results, schedule an appointment to discuss results, or notified of results by mail. Follow up care varies depending on many factors related to your test. Sometimes there is no follow up after you have been notified of test results. At other times follow up may be suggested or necessary. Some examples of follow up care include changes to medication or treatment plans, referral to a specialist, more or less frequent monitoring, and additional tests or procedures. Talk with your healthcare worker about any concerns or questions you have regarding follow up care or instructions.
 Palomaki GE, Bradley LA, & McDowell GA: Technical standards and guidelines: prenatal screening for Down syndrome. Genet Med 2005; 7(5):344-354.
 Akbas SH, Ozben T, Alper O, et al: Maternal serum screening for Down's syndrome, open neural tube defects and trisomy 18. Clin Chem Lab Med 2001; 39(6):487-490.
 Benn PA, Clive JM, & Collins R: Medians for second-trimester maternal serum alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol; differences between races or ethnic groups. Clin Chem 1997; 43(2):333-337.
 Driscoll DA & Nakamura Y: Second trimester maternal serum screening for fetal open neural tube defects and aneuploidy. Genet Med 2004; 6(6):540-541.
 Haddow JE, Palomaki GE, Knight GJ, et al: Prenatal screening for Down's syndrome with use of maternal serum markers. N Engl J Med 1992; 327(9):588-593.