**Core Concept**
The risk of Down syndrome in a pregnancy is influenced by the age of the mother, with advanced maternal age being a significant risk factor. The risk increases with each advancing year of maternal age, especially after the age of 35.

**Why the Correct Answer is Right**
The risk of Down syndrome is directly related to the chromosomal instability that occurs with increasing maternal age. This is due to the increased likelihood of meiotic errors during oocyte maturation, which can lead to aneuploidy, including trisomy 21. The risk of Down syndrome is estimated to be around 1 in 1,250 for women aged 35-39, and 1 in 100 for women aged 45 and above.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the risk of Down syndrome is not significantly increased in women under the age of 35. While the risk is present, it is relatively low, around 1 in 1,500 for women aged 20-24.

**Option B:** This option is incorrect because the risk of Down syndrome is not directly related to the woman's socioeconomic status or lifestyle factors. While these factors may influence overall health and pregnancy outcomes, they do not directly impact the risk of Down syndrome.

**Option C:** This option is incorrect because the risk of Down syndrome is not decreased by any specific medical intervention or treatment. While prenatal testing and screening can identify Down syndrome, these tests do not affect the underlying risk.

**Option D:** This option is incorrect because the risk of Down syndrome is not directly related to the woman's family history. While a family history of Down syndrome may increase the risk, this is not the primary factor influencing the risk in a 35-year-old woman.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the risk of Down syndrome increases significantly after the age of 35, and women in this age group should be offered advanced prenatal testing and screening to assess the risk.

**Correct Answer: C. 1 in 100**