Differences Between NIPT and First-Trimester Combined Screening

NIPT and first-trimester combined screening are two different approaches used to estimate the chance of selected chromosome conditions during pregnancy. Both are screening tests; neither provides a definitive diagnosis on its own.

How is first-trimester combined screening performed?

Combined screening is generally performed between 10 and 13 weeks. It uses two maternal serum markers, the nuchal translucency measurement on ultrasound and factors such as maternal age to calculate the chance of conditions including trisomy 21 and trisomy 18.

Ultrasound is an essential component. Increased nuchal translucency can be associated not only with chromosome conditions but also with certain structural or genetic conditions, so it may provide additional clinical information.

How is NIPT performed?

From 10 weeks, NIPT analyses placental cell-free DNA in maternal blood. It offers higher sensitivity and specificity than traditional serum screening for common fetal aneuploidies. It remains a screening test because the analysed DNA mainly comes from the placenta.

What are the main differences?

Sample and method: Combined screening uses maternal serum markers plus ultrasound. NIPT analyses placental cell-free DNA in maternal blood.
Timing: NIPT can start at 10 weeks. Combined screening depends on a defined ultrasound window, usually 10–13 weeks.
Screening performance: NIPT has stronger screening performance for trisomy 21, 18 and 13, but it is not diagnostic.
Ultrasound information: NIPT does not assess fetal anatomy. First-trimester ultrasound provides information on dating, viability, multiple pregnancy and certain early structural findings.
Next steps: A high-risk result from either approach may need confirmation by CVS or amniocentesis.

Should both screening tests be performed?

Using several independent screening tests for the same chromosome conditions at the same time can produce conflicting risk estimates and unnecessary anxiety. Current guidance supports selecting one prenatal screening approach after counselling. Ultrasound assessment remains an essential part of prenatal care regardless of the blood-based screening method selected.

Which option is appropriate?

The choice depends on gestational age, multiple pregnancy, ultrasound findings, previous pregnancy and family history, test scope and the patient’s preferences about possible next steps. Choosing diagnostic testing directly, or declining testing, can also be part of informed decision-making.