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The First Trimester Double Marker test screens for chromosomal abnormalities — primarily Down syndrome (Trisomy 21), Edwards sy...
Also known as: Double Marker Test · First Trimester Screening · NT Plus Biochemistry · Maternal Serum Screening · Down Syndrome Blood Test
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*Inclusive of home collection charges
The First Trimester Double Marker test screens for chromosomal abnormalities — primarily Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13) — in early pregnancy. It measures two maternal serum markers: Free beta-hCG (Free beta human chorionic gonadotropin) and PAPP-A (Pregnancy-Associated Plasma Protein-A), and combines the results with the NT (Nuchal Translucency) measurement from an ultrasound scan to calculate individual risk. This combined first-trimester screening is the recommended approach for all pregnant women, ideally performed between 11 and 13+6 weeks of gestation. No fasting required.
Key benefits of this package include:
What Does the 1st Trimester Down Syndrome Screening — Double Marker Test Measure?
| Level / Result | Possible Interpretation |
|---|---|
| Risk < 1:1000 (Low risk) | Screen negative — low probability of chromosomal abnormality; routine antenatal care continues |
| Risk 1:250 to 1:1000 (Intermediate risk) | Intermediate — counselling recommended; NIPT (Non-Invasive Prenatal Testing) may be offered before considering invasive testing |
| Risk ≥ 1:250 (Screen positive — high risk) | Screen positive — genetic counselling and offer of diagnostic testing (CVS or amniocentesis) recommended |
| Low PAPP-A (< 0.5 MoM) + Low free beta-hCG | Trisomy 18 (Edwards syndrome) pattern — higher risk; specialist referral required |
| High free beta-hCG (> 2.0 MoM) + Low PAPP-A | Down syndrome pattern — combined with NT for final risk calculation |
Important Note: A screen-positive result does NOT diagnose Down syndrome — it identifies pregnancies with elevated statistical risk requiring further evaluation. The false-positive rate is approximately 5% — meaning 1 in 20 screen-positive results will be in a chromosomally normal pregnancy. Conversely, 10–15% of Down syndrome pregnancies may screen negative. Definitive diagnosis requires karyotyping from CVS (weeks 11–13) or amniocentesis (weeks 15–20). All results require specialist genetic counselling before decisions are made about further testing.
NIPT — The Next Step After a Screen-Positive Double Marker: Non-Invasive Prenatal Testing (NIPT) analyses cell-free foetal DNA in maternal blood, achieving detection rates above 99% for Trisomy 21 with false-positive rates below 0.1% — dramatically superior to the Double Marker. NIPT is increasingly recommended as a second-tier test for screen-positive women (reducing the need for invasive procedures) or as a primary screening option for high-risk women (advanced maternal age, prior chromosomal pregnancy). However, NIPT is a screening test — a positive NIPT result still requires confirmatory CVS or amniocentesis for definitive chromosomal diagnosis before any irreversible decision.
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