NIPT vs Combined First Trimester Screening
If you have had Non-Invasive Prenatal Testing (NIPT), you do not need to undergo Combined First Trimester Screening (CFTS) as NIPT provides superior detection rates for common chromosomal abnormalities with fewer false positives. 1, 2
Comparative Performance of NIPT vs Traditional Screening
- NIPT demonstrates significantly higher positive predictive value (PPV) for trisomy 21 (Down syndrome) at 50-95%, compared to only 2.2-3.6% for traditional first trimester combined screening 1
- This translates to needing only 1.1-2 amniocentesis procedures to confirm trisomy in an affected pregnancy with NIPT, versus 28-45 diagnostic procedures with traditional screening 1
- NIPT achieves superior detection rates for common trisomies with fewer false positives, reducing unnecessary invasive procedures 2, 3
Limitations of NIPT to Consider
- NIPT is a screening test, not a diagnostic test, and any positive result requires confirmation through diagnostic testing (amniocentesis or CVS) 4, 2
- Approximately 1% of NIPT samples result in "no-call" results, most commonly due to insufficient fetal fraction 1, 2
- NIPT does not screen for neural tube defects or other structural abnormalities, which are partially assessed during the ultrasound component of CFTS 1, 2
When Additional Testing May Be Warranted
- If NIPT yields a "no-call" result, repeat testing provides a result in 75-80% of cases when performed at a later gestational age 1, 2
- Some studies have shown a higher rate of chromosomal abnormalities in pregnancies with "no-call" results, though evidence is mixed 1
- The American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine recommend offering diagnostic testing to individuals with a "no-call" result 1
Benefits of NIPT Over CFTS
- Higher detection rates for common trisomies (trisomy 21,18, and 13) 2, 3
- Lower false-positive rates, resulting in fewer unnecessary invasive procedures 1, 2
- Earlier screening in twin pregnancies is beneficial, as NIPT performance in twins is equivalent to singletons 1, 2
- Earlier results allow for more time to consider options and potentially safer procedures if pregnancy termination is elected 1
Pre-test and Post-test Considerations
- Comprehensive pre-test counseling should include discussion of the optional and screening nature of NIPT, types of conditions that can and cannot be detected, and possible test results 1, 2
- Post-test counseling for negative results should emphasize risk reduction but not elimination, and that NIPT only screens for select conditions 1, 2
- Post-test counseling for positive results should include discussion of the PPV of the result and recommendation for diagnostic confirmation 1, 2
In conclusion, while CFTS has historically been the standard screening approach, NIPT offers superior performance for detecting common chromosomal abnormalities. The evidence strongly supports that if you have already had NIPT, additional CFTS would be redundant for aneuploidy detection and would only increase false positive results without significantly improving detection rates 1, 2, 3.