**Question:** Which screening test is not done in pregnant women?

A. Serum Alpha-Fetoprotein (AFP) test
B. Ultrasound scan
C. Thyroid Function Tests (TFTs)
D. Complete Blood Count (CBC)

**Core Concept:** In the context of pregnancy, various screening tests are performed to monitor fetal and maternal health, excluding those that could pose potential risks or interfere with the pregnancy outcome.

**Why the Correct Answer is Right:**

The correct answer, **Thyroid Function Tests (TFTs)**, is not done in pregnant women because:

1. **TFTs assess thyroid function:** These tests measure thyroid hormones (T3 and T4) and thyroid-stimulating hormone (TSH) levels in the blood. In pregnancy, the thyroid hormones increase to support fetal growth, and thyroid-stimulating hormone levels decrease. Performing TFTs can lead to misinterpretation of the results due to the physiological changes during pregnancy.

**Why Each Wrong Option is Incorrect:**

1. **Serum Alpha-Fetoprotein (AFP) test:** AFP is a protein produced by the fetus and placenta during pregnancy. Elevated AFP levels indicate increased risk of certain birth defects (e.g., neural tube defects). This test is performed routinely in pregnancy to screen for such abnormalities.

2. **Ultrasound scan:** An ultrasound scan is a non-invasive imaging test used to visualize the fetus, monitor growth, and detect structural abnormalities. It is a standard procedure during pregnancy and plays a crucial role in prenatal care.

3. **Complete Blood Count (CBC):** A CBC measures the number of red and white blood cells, as well as platelet count, in the blood. Although CBC is performed during pregnancy to monitor anemia, it is generally safe and does not pose significant risks for pregnant women.

**Clinical Pearl:** It is essential to understand the physiological changes in pregnancy and choose appropriate tests to ensure accurate diagnosis and management of maternal and fetal health. Misinterpretation of test results during pregnancy could lead to unnecessary interventions or missed diagnoses. A comprehensive understanding of normal pregnancy physiology is vital for making informed decisions about appropriate screening tests and interventions.