Which of the following statements is false about non-invasive prenatal testing?

Explanation

## Correct Answer: B. It is used for the diagnosis of trisomy 13,18 and 21 Option B is the FALSE statement. Non-invasive prenatal testing (NIPT) is NOT used for diagnosis of chromosomal abnormalities—it is a **screening test**, not a diagnostic test. This is the critical distinction that NBE tests. NIPT detects cell-free fetal DNA (cfDNA) in maternal serum and calculates risk scores for trisomy 21, 18, and 13, but it cannot diagnose these conditions. Diagnosis requires confirmatory testing via amniocentesis or chorionic villus sampling (CVS) with karyotyping or microarray. According to Indian guidelines (ICOG, FOGSI) and international standards (ACOG, RCOG), NIPT is a first-line screening tool with high sensitivity (>99% for trisomy 21) and specificity, but positive results must always be confirmed with invasive testing before counseling or management decisions. The trap is that students often conflate "detection" with "diagnosis"—NIPT detects risk, not disease. In Indian clinical practice, NIPT is increasingly used as a non-invasive alternative to combined first-trimester screening (nuchal translucency + biochemical markers), but it remains a screening modality that requires confirmatory testing for definitive diagnosis. ## Why the other options are wrong **A. It uses cell-free circulating fetal DNA in the maternal serum** — This is TRUE. NIPT is fundamentally based on analysis of cfDNA (also called cell-free fetal DNA or cffDNA) that crosses the placental barrier into maternal circulation. This DNA originates from trophoblastic cells and fetal cells, comprising 3–20% of total cfDNA in maternal serum. This is the scientific foundation of NIPT and is correctly stated. **C. It is done after the routine first trimester ultrasound assessment** — This is TRUE in clinical practice. NIPT is typically offered after first-trimester ultrasound (11–14 weeks) which includes nuchal translucency measurement and dating. This sequence allows counseling based on ultrasound findings before NIPT. Indian protocols recommend this integrated approach for optimal risk stratification and patient counseling. **D. It can be performed after 10 weeks of gestation** — This is TRUE. NIPT can be performed from 10 weeks of gestation onwards (some tests from 9 weeks), when fetal cfDNA fraction is sufficient for reliable analysis. Earlier testing (before 10 weeks) has lower fetal fraction and higher failure rates. This timing is well-established in international and Indian guidelines. ## High-Yield Facts - **NIPT is a screening test, not diagnostic**—positive results require confirmatory testing (amniocentesis/CVS) before diagnosis - **Fetal cfDNA comprises 3–20% of total maternal cfDNA**—higher in multiple gestations and chromosomal abnormalities - **NIPT detects trisomy 21, 18, 13 with >99% sensitivity and >99% specificity**—but positive predictive value varies by maternal age and prevalence - **NIPT can be performed from 10 weeks gestation onwards**—requires adequate fetal fraction (typically >4%) for reliable results - **NIPT is non-invasive alternative to combined first-trimester screening**—reduces need for invasive testing in low-risk pregnancies - **False positive NIPT requires amniocentesis confirmation**—especially important in advanced maternal age and multiple gestations ## Mnemonics **NIPT ≠ Diagnosis (Screen vs Diagnose)** NIPT = **S**creening (cfDNA analysis, risk calculation) → Positive → **D**iagnosis (amniocentesis/CVS karyotype). Remember: NIPT tells you RISK, not DISEASE. Use this when students confuse 'detection' with 'diagnosis'. **NIPT Timing: 10+ weeks** **10 weeks** = minimum gestation for NIPT (adequate fetal fraction). Before 10 weeks = low cfDNA fraction = high failure rate. Think '10 = minimum' for quick recall. ## NBE Trap NBE pairs NIPT with "diagnosis" to trap students who conflate screening with diagnostic testing. The question tests whether students understand that NIPT is a risk-assessment tool requiring confirmatory invasive testing, not a definitive diagnostic modality. ## Clinical Pearl In Indian antenatal clinics, NIPT is increasingly offered as a non-invasive first-line screening after first-trimester ultrasound. However, counseling must emphasize that a positive NIPT (e.g., high risk for trisomy 21) is NOT a diagnosis—it mandates amniocentesis for karyotyping before any management decisions (termination, in-utero therapy, or preparation for postnatal care). This distinction prevents unnecessary anxiety and inappropriate interventions. _Reference: DC Dutta's Textbook of Obstetrics (Prenatal Diagnosis chapter); ICOG Guidelines on Prenatal Screening; Harrison Ch. 424 (Genetic Counseling)_