Frequency of Down syndrome increases when the maternal age is :

Options

A. Below 35 years
B. Above 35 years
C. At the time of first pregnanacy
D. After bearing three children

Answer

**Step-by-Step Solution:**

1. **Understanding Down Syndrome**: Down syndrome is a genetic disorder caused by the presence of an extra chromosome 21, leading to a condition known as trisomy 21. Normally, humans have 46 chromosomes, but individuals with Down syndrome have 47 chromosomes.

2. **Maternal Age and Down Syndrome**: Research indicates that the frequency of Down syndrome increases with maternal age. As women age, particularly after the age of 35, the risk of chromosomal abnormalities in their eggs increases.

3. **Chromosomal Abnormalities**: The increase in risk is attributed to several factors, including the likelihood of chromosomal translocations and improper cell division as women age. These factors can lead to the formation of eggs with an abnormal number of chromosomes.

4. **Evaluating the Options**:
- **Below 35 years**: This option is incorrect as the risk of Down syndrome is lower in younger mothers.
- **Above 35 years**: This option is correct. Studies show that women over 35 have a higher risk of having a child with Down syndrome.
- **At the time of first pregnancy**: This option is also incorrect as the risk is more related to the age of the mother rather than the timing of her first pregnancy.
- **After bearing three children**: This option is incorrect as the number of previous pregnancies does not influence the risk of Down syndrome.

5. **Conclusion**: The correct answer is that the frequency of Down syndrome increases when the maternal age is above 35 years.

---