Detection of aneuploidy in 1st trimester:
**Core Concept**
The first trimester screening for aneuploidy involves a combination of ultrasound markers and serum biomarkers to assess the risk of chromosomal abnormalities, such as Down syndrome, trisomy 13, and trisomy 18. This screening aims to identify pregnancies with a higher risk of aneuploidy, allowing for further diagnostic testing and informed decision-making.
**Why the Correct Answer is Right**
The first trimester screening involves the measurement of two key serum biomarkers: human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein-A (PAPP-A). hCG is a hormone produced by the placenta, and elevated levels are associated with an increased risk of Down syndrome. PAPP-A is a protein produced by the placenta, and low levels are associated with an increased risk of Down syndrome. The combination of these two biomarkers has been shown to be a reliable predictor of aneuploidy in the first trimester. The measurement of these biomarkers is typically performed between 11 and 14 weeks of gestation.
**Why Each Wrong Option is Incorrect**
**Option B:** hCG and AFP (alpha-fetoprotein) are both markers used in the second trimester screening for aneuploidy, but they are not used in combination in the first trimester screening. AFP is not a reliable marker for first trimester screening.
**Option C:** The addition of AFP to the first trimester screening does not improve the detection rate of aneuploidy and is not recommended. The combination of hCG and PAPP-A is sufficient for first trimester screening.
**Option D:** Estriol is a hormone produced by the placenta, but it is not used in the first trimester screening for aneuploidy. Estriol is one of the biomarkers used in the quad screen, which is performed in the second trimester.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the first trimester screening for aneuploidy is not a diagnostic test, but rather a screening test that identifies pregnancies with a higher risk of aneuploidy. Further diagnostic testing, such as chorionic villus sampling (CVS) or amniocentesis, is necessary to confirm the presence of aneuploidy.
**✓ Correct Answer: A. hCG and PAPP-A**