**Core Concept**
Congenital rubella syndrome (CRS) is a condition that occurs when a fetus is infected with the rubella virus in utero, leading to various congenital anomalies. The risk of damage to the fetus is highest when the maternal infection occurs during the first trimester, particularly during the critical period of organogenesis.

**Why the Correct Answer is Right**
The risk of CRS is maximum if the mother gets infected with rubella between 6-12 weeks of pregnancy. This period corresponds to the first trimester, when the fetus's major organs and systems are developing. The rubella virus can cause damage to the developing fetus by disrupting the normal development of these organs, leading to congenital anomalies such as deafness, cataracts, and heart defects. The virus can also cause miscarriage or stillbirth if the infection is severe.

**Why Each Wrong Option is Incorrect**
**Option A:** Infection at 20-24 weeks of pregnancy is still a concern, but the risk of CRS is significantly lower compared to infections occurring during the first trimester. The fetus's major organs have already formed, and the risk of congenital anomalies is reduced, although the risk of miscarriage or stillbirth remains.
**Option B:** Infection at 24-28 weeks of pregnancy is even less likely to cause CRS, as the fetus's organs are almost fully formed, and the risk of congenital anomalies is minimal.
**Option C:** Infection at 32-36 weeks of pregnancy poses little to no risk of CRS, as the fetus's organs are fully formed, and the risk of congenital anomalies is extremely low.

**Clinical Pearl / High-Yield Fact**
The risk of CRS can be significantly reduced if the mother is vaccinated against rubella before pregnancy or receives post-exposure prophylaxis if she is exposed to the virus during pregnancy. This highlights the importance of rubella vaccination in preventing CRS and its associated congenital anomalies.

**✓ Correct Answer: D. 6-12 weeks of pregnancy**