Maternal Serum Screening, Second Trimester
- Also Known As:
- AFP Maternal
- Maternal Serum AFP
- MSAFP
- msAFP
- Triple Screen
- Triple Test
- Quad Screen
- Quadruple Marker Test
- 4-marker Screen
- Multiple Marker Test
- Formal Name:
- Maternal Serum Screen

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At a Glance
Why Get Tested?
For pregnant women, to assess the risk of having a baby with certain chromosomal disorders, such as Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18), or open neural tube defects, such as spina bifida
When To Get Tested?
Usually between the 15th and 20th weeks of pregnancy
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
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The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
What is being tested?
Maternal serum screening, or the multiple marker test, measures several substances in the blood of a pregnant woman in the second trimester of pregnancy. The results can be used to determine the risk that the baby has a chromosome disorder or neural tube defect such as spina bifida.
These substances include the following, listed below. When the first three substances are measured together, it is called a triple screen. When the fourth substance, inhibin A, is added, it is called a quad screen.
- Alpha-fetoprotein (AFP) is a protein produced by fetal tissue. During development, AFP levels in fetal blood and amniotic fluid rise until about 12 weeks, and then levels gradually fall until birth. Some AFP crosses the placenta into the mother’s blood. With certain problems affecting a baby, an increased amount of AFP leaks into amniotic fluid and then into the mother’s blood. As such, an AFP test is used to screen for neural tube defects such as spina bifida. It may be performed as part of the triple or quad screen. It may be performed by itself when risk for chromosome disorders (Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18)) have already been assessed using first trimester Down syndrome screening or cell-free fetal DNA testing. According to the American College of Obstetricians and Gynecologists (ACOG), the AFP test detects neural tube defects in 85% of the cases.
- Human chorionic gonadotropin (hCG) is a hormone produced by the placenta. Levels in maternal blood rise for the first trimester of pregnancy and then decrease during the remainder of the pregnancy. In pregnancies where the fetus is carrying the chromosomal defect that results in Down syndrome, hCG tends to be high whereas in pregnancies where the fetus has the chromosomal defect that results in Edwards syndrome, hCG tends to be low.
- Unconjugated estriol (uE3) is a form of estrogen that is produced by the fetus through metabolism. This process involves the liver, adrenals, and the placenta. Some of the unconjugated estriol crosses the placenta and can be measured in the mother’s blood. Levels rise around the 8th week and continue to increase until shortly before delivery. In pregnancies where the fetus has Down syndrome or Edwards syndrome, uE3 tends to be low.
- Inhibin A is a hormone produced by the placenta. Inhibin is a dimer (has two parts) and is sometimes referred to as DIA or dimeric inhibin A. Levels in maternal blood decrease slightly from 14 to 17 weeks gestation and then rise again. Levels tend to be higher in pregnancies where the fetus has Down syndrome.
Including the fourth marker, inhibin A, increases both the sensitivity and specificity of the screen for Down syndrome. According to ACOG, the triple screen detects Down syndrome in 69% of the cases while the quad screen detects it in 81% of the cases.
If the results of maternal serum screening are cause for concern, diagnostic tests such as amniocentesis or chorionic villus sampling (CVS) may be recommended.
Common Questions
View Sources
Sources Used in Current Review
(2014 April). American College of Obstetricians and Gynecologists. Screening tests for birth defects, FAQ. Available online at http://www.acog.org/Patients/FAQs/Screening-Tests-for-Birth-Defects. Accessed 12/26/2016.
(2015 September). American College of Obstetricians and Gynecologists. Committee Opinion, Number 640. Available online at http://www.acog.org/Resources-And-Publications/Committee-Opinions/Committee-on-Genetics/Cell-free-DNA-Screening-for-Fetal-Aneuploidy. Accessed 12/26/2016.
Mayo Clinic staff. (2015 October 21). Quad screen. Mayo Clinic. Available online at http://www.mayoclinic.com/health/quad-screen/MY00127. Accessed 12/26/2016.
(Reviewed 2016 April 21). Centers for Disease Control and Prevention. Folic acid, recommendations. Available online at https://www.cdc.gov/ncbddd/folicacid/recommendations.html. Accessed 12/26/2016.
(2016 May). American College of Obstetricians and Gynecologists. Practice Bulletin Number 163: Screening for fetal aneuploidy. Available online at https://s3.amazonaws.com/cdn.smfm.org/publications/224/download-491f0e6962960848d2097447ab57a024.pdf. Accessed 12/26/2016.
(2016 September). American College of Obstetricians and Gynecologists. Screening for birth defects. Available online at http://www.acog.org/~/media/For%20Patients/faq165.pdf?dmc=1&ts=20130213T1410405774. Accessed 12/26/2016.
(2016 October). March of Dimes. Down syndrome. Available online at http://www.marchofdimes.com/baby/birthdefects_downsyndrome.html. Accessed 12/26/2016.
(Reviewed 2016 October 20). Centers for Disease Control and Prevention. Birth defects, diagnosis. Available online at http://www.cdc.gov/ncbddd/birthdefects/diagnosis.html. Accessed 12/26/2016.
(© 1995-2016). Mayo Medical Laboratories. Quad screen (second trimester) maternal, serum. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/81149. Accessed 12/26/2016.
(© 2016). Trisomy 18 Foundation. What is trisomy 18? Available online at http://www.trisomy18.org/site/PageServer?pagename=whatisT18_whatis. Accessed 12/26/2016.
(© 2016). Quest Diagnostics Test Center. Prenatal Screening and Diagnosis of Neural Tube Defects, Down Syndrome, and Trisomy 18. Available online at http://www.questdiagnostics.com/testcenter/testguide.action?dc=CF_PrenatScreen. Accessed January 2017.
(September 2016) American Congress of Obstetricians and Gynecologists. Prenatal Genetic Screening Tests. Available online at http://www.acog.org/Patients/FAQs/Prenatal-Genetic-Screening-Tests?IsMobileSet=false. Accessed January 2017.
Sources Used in Previous Reviews
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Trisomy 18 Foundation. Available online at http://www.trisomy18.org. Accessed September 2010.
Barclay, L. and Lie, D. (Reviewed 2008 January 3). New Guidelines Recommend Universal Prenatal Screening for Down Syndrome. Medscape Medical News [on-line CME]. Available online at http://www.medscape.com/viewarticle/550256. Accessed September 2010.
Trisomy 18 Foundation. What is Trisomy 18? Available online at http://www.trisomy18.org/site/PageServer?pagename=whatisT18_whatis. Accessed February 2013.
March of Dimes. Birth defects: Down syndrome. Available online at http://www.marchofdimes.com/baby/birthdefects_downsyndrome.html. Accessed February 2013.
Centers for Disease Control and Prevention. Folic Acid Recommendations. Available online at http://www.cdc.gov/ncbddd/folicacid/recommendations.html. Accessed February 2013.
Centers for Disease Control and Prevention. Birth Defects, Diagnosis. Available online at http://www.cdc.gov/ncbddd/birthdefects/diagnosis.html. Accessed February 2013.
ACOG. Screening for Birth Defects. Available online at http://www.acog.org/~/media/For%20Patients/faq165.pdf?dmc=1&ts=20130213T1410405774. Accessed February 2013.
KidsHealth.org. What is the Multiple Marker Test? Available online at http://kidshealth.org/parent/system/medical/triple_screen.html. Accessed February 2013.
MayoClinic.com. Quad screen. Available online at http://www.mayoclinic.com/health/quad-screen/MY00127. Accessed February 2013.
ARUP Laboratories. Maternal Serum Screen, Alpha Fetoprotein, hCG, and Estriol. Available online at http://www.aruplab.com/guides/ug/tests/0080108.jsp. Accessed February 2013.
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