Risk of having a child with Down syndrome:
**Core Concept:** Down syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. It is associated with developmental delays, intellectual disability, and characteristic physical features. The risk factors for Down syndrome during pregnancy include maternal age and the presence of trisomy 21 in the fetus.
**Why the Correct Answer is Right:** The correct answer, **C. 1 in 1,000 pregnancies**, represents the estimated prevalence of Down syndrome in newborns. The risk increases significantly with the mother's age, as the probability of having a child with Down syndrome is 1 in 1,000 for women under 35 years old. However, for women aged 40 and above, the risk is much higher.
**Why Each Wrong Option is Incorrect:**
A. **1 in 1,000,000 pregnancies (0.0009%)** is too low and does not accurately represent the actual risk.
B. **1 in 1,000 pregnancies (0.1%)** is still too low and does not account for the increased risk associated with maternal age.
D. **1 in 100 pregnancies (10%)** is an overestimation of the actual risk and does not consider the maternal age factor.
**Clinical Pearl:**
The risk of having a child with Down syndrome is a critical piece of information for expecting parents and healthcare providers to discuss. It is essential to consider the mother's age when assessing the likelihood of having a child with Down syndrome, as age-related risks increase significantly. This knowledge empowers parents to make informed decisions about prenatal testing and pregnancy management, as well as contributes to public health initiatives aimed at early detection and intervention for affected infants, enabling better healthcare planning and resource allocation.