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The triple test and quad screen are second-trimester maternal serum screening tests used to assess the risk of chromosomal abnormalities and neural tube defects in a developing fetus. The triple test measures three markers — alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3) — and detects approximately 65-70% of Down syndrome cases. The quad screen adds a fourth marker, inhibin A, increasing detection to approximately 80-85%. Both tests are performed between 15-20 weeks of pregnancy, have false positive rates of 5-8%, and report results as age-adjusted risk ratios. The quad screen is the preferred test when available because it provides superior detection with the same blood draw. This guide provides a detailed comparison of both tests, including what they measure, their detection rates, when they are performed, cost differences, insurance coverage, and what happens after a positive screen.
A Non-Stress Test (NST) is a simple, painless prenatal test that monitors fetal heart rate patterns and accelerations to assess fetal well-being in the third trimester. This test measures fetal heart rate response to movement, evaluating oxygen delivery and neurological development. Understanding what NST measures, when it's recommended, how to interpret results, and what abnormal findings mean helps expectant mothers navigate this common aspect of high-risk pregnancy monitoring.
The maternal serum AFP test is a second-trimester blood screening performed between 15 and 20 weeks of pregnancy that measures alpha-fetoprotein, a protein produced by the fetal liver, to assess risk for open neural tube defects, abdominal wall defects, and chromosomal abnormalities. As part of the quad screen, it achieves approximately 81% detection of Down syndrome and 80% detection of open neural tube defects at a 5% false-positive rate, according to ACOG Practice Bulletin No. 226. This complete guide covers screening timelines, what each marker measures, comparison with NIPT, and what happens after screening.
The normal maternal serum AFP range in pregnancy is 0.5 to 2.0 Multiple of the Median (MoM) between 15 and 20 weeks gestation, a standardized value adjusted for gestational age, maternal weight, diabetes status, race, and other factors. Approximately 95% of unaffected pregnancies fall within this range. Understanding how MoM is calculated, what factors influence your result, and the sensitivity and specificity of AFP screening can help you interpret your test with confidence.
An elevated maternal serum AFP level above 2.0 MoM (Multiple of the Median) occurs in approximately 3-5% of pregnancies and triggers a diagnostic evaluation for open neural tube defects, abdominal wall defects, and other fetal conditions. However, 80-85% of pregnancies with elevated AFP result in healthy babies, with incorrect gestational age dating accounting for 30-40% of elevated results. This guide provides a comprehensive differential diagnosis, the evidence-based follow-up algorithm, ultrasound and amniocentesis decision-making, and practical guidance for navigating the evaluation process.
Alpha-fetoprotein (AFP) plays a counterintuitive role in Down syndrome screening: AFP levels are LOWER in pregnancies affected by Down syndrome, not higher. This finding, combined with measurements of hCG, estriol, and sometimes inhibin A, forms the basis of the triple and quad screen tests performed at 15-20 weeks of pregnancy. The triple screen detects approximately 65-70% of Down syndrome cases, while the quad screen improves detection to approximately 80-85%. However, both have significant false positive rates of 5-8%. Non-invasive prenatal testing (NIPT), which analyzes cell-free fetal DNA, has largely replaced serum screening with a detection rate above 99% and a false positive rate below 0.5%. This guide explains how AFP fits into Down syndrome screening, compares the accuracy of different screening methods, and helps you understand the best testing strategy for your pregnancy.
