NIPT vs NT Scan vs Double Marker Test: Key Differences

Early pregnancy screening helps estimate the chance that a baby has a chromosomal condition such as Down syndrome. The three tests most often discussed are the NT scan, the double marker blood test and NIPT. They work differently, are done at slightly different times and have different accuracy.

What Is the NT Scan?

Nuchal translucency (NT) is a small fluid space at the back of the baby's neck. An increased measurement can be associated with chromosomal conditions, heart problems and some other conditions. The scan, done between about 11 and 14 weeks, also checks the baby's heartbeat, dating, number of babies and early anatomy, and may assess the nasal bone and blood flow.

What is the double marker test?

The double marker test measures PAPP-A and free beta hCG in the mother's blood. Results are combined with the NT measurement, maternal age and other factors to calculate a risk score for trisomy 21, 18 and 13. This combined approach detects most, but not all, cases.

What Is NIPT?

Non-invasive prenatal testing analyses cell-free DNA that comes mainly from the placenta and circulates in the mother's blood. It can be done from about 10 weeks. It screens mainly for trisomy 21, 18 and 13, and some panels include other conditions. NIPT has a high detection rate and a lower false-positive rate than combined screening for trisomy 21.

How do the tests compare?

| Feature | NT scan | Double marker | NIPT |

|---|---|---|---|

| Type | Ultrasound | Blood test | Blood test |

| Timing | About 11 to 14 weeks | About 9 to 13 weeks | From about 10 weeks |

| Main purpose | Neck fluid, early anatomy | Hormone markers | Placental DNA analysis |

| Accuracy for Down syndrome | Better when combined | Better when combined | Highest of the three |

| Detects structural problems | Some early ones | No | No |

| Diagnostic? | No | No | No |

Why is the NT scan still important with NIPT?

NIPT does not examine the baby's structure. The NT scan can detect early anatomical problems, increased NT linked to heart defects and other conditions, and confirm dating and twins. Many specialists recommend an NT scan even when NIPT is done.

What happens after a high-risk result?

A high-risk result from any screening test needs counselling and usually a diagnostic test such as chorionic villus sampling (CVS) or amniocentesis before any decisions are made.

Which test is right for you?

The choice depends on your age, history, previous results, twin pregnancy, cost and personal preferences. Your fetal medicine specialist will explain options. In India, sex determination is prohibited by law, so fetal sex is not disclosed.

A few things to hold on to

Understanding each test helps you choose the screening that suits your pregnancy. Counselling before and after testing is important. Dr Malathi G. Prasad offers first-trimester screening and fetal medicine counselling in Trichy.

To arrange this at our Trichy centre, see NIPT; if you are unsure whether you need it, our doctors can tell you after a review.

Related guides

• What Does a High-Risk NIPT Result Mean?
• NIPT in Twin Pregnancy: Is It Reliable?
• Can NIPT Detect Down Syndrome?