**Question:** Risk of damage to fetus by maternal rubella is maximum if mother gets infected in

A. First trimester
B. Second trimester
C. Third trimester
D. Post-partum period

**Core Concept:** Rubella, also known as German Measles, is a viral infection caused by the Rubella virus. If a pregnant woman gets infected with rubella, the risk of congenital rubella syndrome (CRS) in the developing fetus increases as the gestational age advances. CRS is a group of severe birth defects and impairments caused by maternal rubella infection during pregnancy.

**Why the Correct Answer is Right:** The risk of damage to the fetus due to maternal rubella infection is highest when the mother gets infected during the **first trimester**. This is because the first trimester is when major organ systems of the fetus are developing rapidly. If the infection occurs during this period, it can cause severe birth defects and malformations due to the virus's direct impact on fetal tissues and organs and also due to the virus's interference with the fetal immune system development.

**Why Each Wrong Option is Incorrect:**

A. **Second trimester**: While infection in the second trimester still poses risks, the severity of birth defects is generally less compared to the first trimester. This is because the critical organogenesis phase is mostly over by the second trimester.

B. **Third trimester**: Although the risk of fetal complications is lower in the third trimester, infection during this stage can still lead to premature labor and low birth weight, which can have significant health implications for the newborn.

C. **Post-partum period**: Infection post-delivery primarily affects the mother, not the fetus. However, if the mother gets infected during pregnancy and then becomes pregnant again soon after giving birth, there is a higher risk of infecting the new fetus.

**Clinical Pearl:** Vaccinating against rubella is crucial in preventing maternal rubella infection and its associated congenital defects. In high-risk countries, universal vaccination programs are implemented to protect pregnant women and reduce CRS cases. In case of unvaccinated pregnant women, timely diagnosis and referral for isolation and treatment are essential to minimize the risk to the fetus.