Quadruple testing is done during:

Explanation

## Correct Answer: A. 15-20 weeks Quadruple testing (also called quadruple marker screening or quad screen) is a second-trimester biochemical screening test performed between **15–20 weeks of gestation**, with optimal timing at **16–18 weeks**. This test measures four maternal serum markers: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin A. The timing is critical because marker levels change predictably with gestational age; accurate dating is essential for correct interpretation. In India, per IAP and FOGSI guidelines, quad screening is offered as part of aneuploidy risk assessment, particularly for Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). The detection rate for Down syndrome is approximately 80% with a false-positive rate of 5%. This test is preferred over triple screening (which omits inhibin A) because the addition of inhibin A increases detection sensitivity. Quad screening is non-invasive, safe, and cost-effective, making it the standard of care in Indian obstetric practice for risk stratification before offering invasive testing (amniocentesis or chorionic villus sampling) if indicated. ## Why the other options are wrong **B. 22-28 weeks** — This window falls in the third trimester and is too late for quad screening. By 22–28 weeks, marker levels have changed significantly, making interpretation unreliable. This timing is appropriate for other antenatal assessments (growth scan, Doppler studies) but not for biochemical screening. NBE may trap students who confuse second-trimester screening timing with third-trimester ultrasound windows. **C. 9-11 weeks** — This is the first-trimester window (9–13 weeks) used for **combined screening** (PAPP-A + β-hCG + nuchal translucency ultrasound), not quad screening. Quad screening is exclusively a second-trimester test. Students may confuse first-trimester combined screening with second-trimester quad screening, a common NBE trap in aneuploidy screening questions. **D. 12-14 weeks** — This overlaps the end of first trimester and early second trimester but is too early for quad screening. At 12–14 weeks, the four markers (especially inhibin A and uE3) have not reached reliable levels for accurate interpretation. This timing is sometimes used for early anatomy scan but not for quad marker assessment. ## High-Yield Facts - **Quad screen timing: 15–20 weeks** (optimal 16–18 weeks) — second-trimester biochemical test for aneuploidy risk. - **Four markers in quad screening:** AFP, hCG, uE3, and inhibin A — inhibin A addition increases Down syndrome detection to ~80%. - **Down syndrome pattern:** ↓AFP, ↑hCG, ↓uE3, ↑inhibin A — quad screen detects ~80% with 5% false-positive rate. - **Combined screening (first trimester):** 11–13 weeks with PAPP-A + β-hCG + nuchal translucency — different from quad screening. - **Accurate dating essential:** Gestational age accuracy ±3–5 days required; ultrasound confirmation mandatory before quad screening interpretation. - **Indian guidelines (FOGSI/IAP):** Quad screening offered as non-invasive risk assessment; abnormal results warrant genetic counseling and consideration of invasive testing. ## Mnemonics **QUAD = 15–20 weeks (Second Trimester)** **Q**uadruple = **Q**uarter (2nd trimester = weeks 15–20). Remember: First trimester (9–13 weeks) = Combined screening; Second trimester (15–20 weeks) = Quad screening. Use this to distinguish between the two major aneuploidy screening windows. **AFP-hCG-uE3-Inhibin A (Down Syndrome Pattern)** **DOWN = Down, hCG Up, uE3 down, Inhibin A up.** In Trisomy 21: AFP ↓, hCG ↑, uE3 ↓, Inhibin A ↑. This pattern is tested frequently in NEET PG and helps recall both the markers and their direction of change. ## NBE Trap NBE commonly pairs "quad screening" with "first-trimester timing" (9–11 weeks) to trap students who confuse quad screening with combined first-trimester screening (PAPP-A + β-hCG + nuchal translucency). The key discriminator is that quad screening is exclusively second-trimester and requires all four serum markers. ## Clinical Pearl In Indian obstetric practice, quad screening is often the first-line non-invasive aneuploidy assessment offered at the 16–18 week routine antenatal visit. An abnormal quad screen (risk >1:250) triggers genetic counseling and discussion of invasive testing (amniocentesis), which carries a small miscarriage risk (~0.1–0.3%). Accurate dating by first-trimester ultrasound is non-negotiable; many false positives in Indian settings arise from incorrect gestational age assignment. _Reference: DC Dutta's Textbook of Obstetrics (7th ed.), Ch. 9 (Antenatal Care); FOGSI Guidelines on Aneuploidy Screening in India_