Quad Screen (AFP Plus)
Second trimester blood test measuring four substances to screen for Down syndrome and neural tube defects.
📅 When Performed
Weeks 15-22, ideally 16-18 weeks
⏱️ Results Timeline
1 week
Overview
The quad screen is a second-trimester blood test that measures four substances produced by the baby and placenta: AFP (alpha-fetoprotein), hCG, estriol, and inhibin-A. The levels of these substances, combined with your age and other factors, provide a risk assessment for certain birth defects.
This test can screen for Down syndrome, trisomy 18, and neural tube defects like spina bifida. It's been largely replaced by NIPT for chromosomal screening, but it's still valuable for detecting neural tube defects, which NIPT cannot screen for.
The quad screen is an older screening option but is still commonly used, especially for women who don't opt for first trimester screening or NIPT.
🎯 Purpose of Test
- •Screen for Down syndrome (trisomy 21)
- •Screen for trisomy 18
- •Detect neural tube defects (spina bifida, anencephaly)
- •Screen for abdominal wall defects
- •Provide risk assessment in second trimester
- •Alternative or addition to first trimester screening
🔬 How It's Performed
- 1.Simple blood draw from arm
- 2.Best performed at 16-18 weeks
- 3.Lab measures AFP, hCG, estriol, and inhibin-A levels
- 4.Results analyzed along with age, weight, and gestational age
- 5.Computer calculates individual risk
- 6.Results ready in about 1 week
👀 What to Expect
- →Quick, routine blood draw
- →No fasting required
- →Can be done at regular prenatal appointment
- →Results in about 1 week
- →Risk assessment provided, not diagnosis
- →High-risk result may warrant ultrasound or amniocentesis
- →Low-risk result provides reassurance
✓ Normal Results
Low risk (less than 1 in 250-300) for all conditions screened
⚠️ Abnormal Results
- •High risk for Down syndrome (1 in 250 or higher)
- •Elevated AFP suggesting neural tube defect
- •High risk for trisomy 18
- •Need for detailed ultrasound to rule out defects
- •May be offered amniocentesis for definitive diagnosis
- •Meet with genetic counselor
- •Elevated AFP can also indicate twins, incorrect dating, or other issues
⚠️ Risks & Considerations
- •No physical risks - just blood draw
- •High false-positive rate (5% get abnormal result)
- •Anxiety from abnormal results
- •May lead to unnecessary further testing
- •Many abnormal results turn out to be false alarms
📝 How to Prepare
- →No fasting or special preparation
- →Accurate dating (by early ultrasound) important for interpretation
- →Schedule between 15-22 weeks
- →Discuss with provider if appropriate for you
- →Understand limitations and false-positive rate
- →Consider if you'll pursue further testing if abnormal