First Trimester Down's Syndrome Screening Markers

First-trimester screening for Down's syndrome aims to identify pregnancies at increased risk using specific markers measured between 11 and 14 weeks of gestation.

Included Screening Markers

• 1. Nuchal translucency (NT): This is an ultrasound measurement of the fluid collection behind the fetal neck. An increased NT measurement is associated with a higher risk of Down's syndrome.
• 2. PAPP-A: This stands for Pregnancy-Associated Plasma Protein-A, a protein produced by the placenta. Lower-than-expected levels of PAPP-A are associated with an increased risk of Down's syndrome.

Excluded Screening Markers

• 3. GTT (Glucose Tolerance Test): This test is used to screen for gestational diabetes and is typically performed later in pregnancy, not during the first trimester for Down's syndrome screening.
• 4. Inhibin A: While a biochemical marker, Inhibin A is primarily used in the second-trimester screening (quad screen), not typically in the first-trimester combination screening.

Therefore, the markers included in the first-trimester screening for Down's syndrome are Nuchal translucency and PAPP-A.