**Core Concept**
The question is testing the understanding of screening tests used to detect cell defects, which are essential in various medical specialties, including genetics and pediatrics. These tests help identify genetic mutations or chromosomal abnormalities that can lead to developmental disorders or increased susceptibility to certain diseases.

**Why the Correct Answer is Right**
Screening tests for cell defects typically involve analyzing blood samples or other tissues for specific genetic markers or chromosomal abnormalities. One common approach is to use **karyotyping**, which involves examining the number and structure of chromosomes. Another method is **molecular genetic testing**, which can identify specific gene mutations or deletions associated with cell defects. These tests are crucial for early diagnosis and management of conditions like Down syndrome, Turner syndrome, or Fragile X syndrome.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to screening tests for cell defects. While it's true that some genetic disorders can be diagnosed through ultrasound, this is not a primary method for detecting cell defects.
* **Option B:** This option is incorrect because **PCR (Polymerase Chain Reaction)** is a molecular genetic testing technique, but it's not a screening test for cell defects. PCR is typically used to amplify specific DNA sequences for further analysis.
* **Option C:** This option is also incorrect because **fluorescence in situ hybridization (FISH)** is a molecular cytogenetic technique used to detect specific genetic abnormalities, but it's not a primary screening test for cell defects.

**Clinical Pearl / High-Yield Fact**
One key point to remember is that screening tests for cell defects should be performed in a timely manner to enable early intervention and management of associated conditions. This can significantly improve patient outcomes and quality of life.

**Correct Answer:** C. FISH (Fluorescence in situ hybridization) is a common screening test used to detect chromosomal abnormalities and cell defects.