As an isolated finding, highest risk of Downs Syndrome is seen with?
**Core Concept**
Downs Syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21 or a significant part of it. The risk of Downs Syndrome is influenced by various factors, including maternal age, family history, and genetic markers.
**Why the Correct Answer is Right**
The risk of Downs Syndrome increases with maternal age, particularly after the age of 35. This is because the error rate of meiosis increases with age, leading to an increased likelihood of nondisjunction, where the chromosomes fail to separate properly during cell division. This results in the formation of an abnormal gamete with an extra copy of chromosome 21. The likelihood of Downs Syndrome is directly correlated with the risk of meiotic errors, which increases with advancing maternal age.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the risk of Downs Syndrome.
* **Option B:** While certain genetic markers, such as the presence of a family history of Downs Syndrome or a history of previous pregnancy with a child with Downs Syndrome, can increase the risk, they do not directly correlate with the risk as much as maternal age does.
* **Option C:** This option is not a recognized risk factor for Downs Syndrome.
**Clinical Pearl / High-Yield Fact**
Maternal age is a significant risk factor for Downs Syndrome, and the risk increases exponentially after the age of 35. This is why older women are often offered screening tests, such as ultrasound and non-invasive prenatal testing (NIPT), to assess the risk of Downs Syndrome.
**Correct Answer: C. Advanced maternal age.