Conducted during the first trimester (usually between 10–14 weeks of pregnancy).

Measures two key markers in maternal blood:

hCG (human chorionic gonadotropin) – hormone produced during pregnancy.

PAPP‑A (pregnancy-associated plasma protein A) – protein produced by the placenta.

Abnormal levels may indicate increased risk of chromosomal abnormalities.

Often combined with nuchal translucency (NT) ultrasound for higher accuracy.

Clinical uses include:

Screening for Down syndrome (Trisomy 21).

Screening for Edwards syndrome (Trisomy 18).

Assessing overall fetal health in early pregnancy.

This is a screening test, not a diagnostic test—positive results require confirmation with further tests (e.g., amniocentesis, chorionic villus sampling).

Analyte: Maternal serum levels of hCG and PAPP‑A.

Normal Findings: Values within expected range for gestational age.

Abnormal Findings:

Low PAPP‑A + high hCG: Suggests increased risk of Down syndrome.

Low PAPP‑A + low hCG: Suggests increased risk of Edwards syndrome.

Clinical Use:

Provides early risk assessment for chromosomal abnormalities.

Helps guide further diagnostic testing and pregnancy management.

Supports informed decision-making for expectant parents.