Detection rate of down syndrome with first trimester screening with NT, PAPP-A and hCG is
**Core Concept**
Down syndrome is a genetic disorder caused by an extra copy of chromosome 21, leading to various physical and developmental abnormalities. First-trimester screening involves measuring nuchal translucency (NT), pregnancy-associated plasma protein-A (PAPP-A), and human chorionic gonadotropin (hCG) levels to assess the risk of Down syndrome.
**Why the Correct Answer is Right**
The combination of NT, PAPP-A, and hCG measurements in the first trimester has been shown to be an effective screening tool for Down syndrome. The NT thickness is a measure of the fluid-filled space at the back of the fetus's neck, which is often increased in Down syndrome cases. PAPP-A is a protein produced by the placenta, and lower levels have been associated with an increased risk of Down syndrome. hCG is a hormone produced by the placenta, and higher levels have been linked to an increased risk of Down syndrome. By combining these markers, the detection rate for Down syndrome can be significantly improved.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the detection rate of Down syndrome with first-trimester screening using NT, PAPP-A, and hCG.
**Option B:** This option is incorrect because it is too low and does not account for the improved detection rate achieved by combining multiple markers.
**Option C:** This option is incorrect because it is too high and not supported by evidence from large-scale studies.
**Clinical Pearl / High-Yield Fact**
When interpreting first-trimester screening results, it is essential to consider the patient's age, as the risk of Down syndrome increases with age. A patient's age should always be taken into account when evaluating the screening results.
**Correct Answer: 85%.**