Aneuploidy Testing
Aneuploidy Overview
1 in 150 live births: Most common disorders include
Trisomy 21 (Down Syndrome): 1 in 800 live births
Trisomy 18 (Edward Syndrome): 1 in 7,000 live births
47 XXY (Klinefelter syndrome): 1 in 500 males
45 X (Turner syndrome): 1 in 20,000 females
Risk factors: Prior aneuploid fetus, increasing maternal age
Testing should be reviewed at first prenatal visit
Screening Options
First Trimester Combined Screen: 11+0 to 13+6 WGA
Screens for trisomy 21 only (85% detection rate)
Measurements/labs include
Nuchal translucency measurement (sonographer skill dependent)
Serum free beta-hCG
Total H-hCG
Pregnancy associated plasma protein A analyte (PAPP-A) levels
Quadruple Screen (AFP Tetra): 15+0 to 22+6 WGA
Screens for trisomy 21 (80% detection rate), trisomy 18, and open fetal defects
Labs include
Serum free beta-hCG
Inhibin A (placental protein)
Unconjugated estriol (uE3 - dominant estrogen produced during pregnancy)
Alpha fetoprotein (AFP - produced by developing liver and yolk sac)
Cell free DNA: 10+0 WGA to term
Information provided
All options tests for trisomy 21 (98% detection), trisomy 18, and trisomy 13, fetal sex
Additional information depends on the specific panel selected
Most commonly used in patients with advanced maternal age, i.e. > 35 years old at time of delivery
Verify insurance coverage before sending test
Sequential Screening Method
Stepwise model: Perform first trimester combined screen
Positive result → perform cfDNA or diagnostic testing
Negative result → perform Quad screen
Contingent model: Perform first trimester combined screen
High risk → perform cfDNA or chorionic villus sampling
Intermediate risk → perform Quad screen
Low risk→ no further screening
Positive Screens
Educate family about condition
Discussion options, e.g. referral to genetics for further counseling, pregnancy termination, referral to a tertiary care center, perinatal hospice, adoption, etc.
More information: See ACOG Bulletin 163