Congenital rubella syndrome is most likely to occur when maternal infection happens during which trimester?

Explanation

## Congenital Rubella Syndrome (CRS) and Trimester Risk **Key Point:** Maternal rubella infection in the **first trimester, particularly before 12 weeks of gestation**, carries the highest risk of congenital rubella syndrome and fetal abnormalities. ### Risk by Trimester | Trimester | Risk of CRS | Defects | Notes | |-----------|-------------|---------|-------| | **First (< 12 weeks)** | 85–90% | Cardiac, ocular, auditory, CNS | Highest teratogenic risk | | **First (12–16 weeks)** | 33% | Primarily deafness | Still significant | | **Second (17–24 weeks)** | 11% | Deafness, eye defects | Lower but present | | **Third (> 24 weeks)** | < 1% | Rare | Minimal risk | ### Classic Triad of CRS 1. **Cardiac defects** (patent ductus arteriosus, pulmonary artery stenosis) 2. **Ocular defects** (cataracts, retinopathy, glaucoma) 3. **Auditory defects** (sensorineural hearing loss) **Mnemonic:** **PCA** = **P**atent ductus arteriosus, **C**ataracts, **A**uditory defects (the "big three" of CRS). **Clinical Pearl:** Rubella IgM serology in the first trimester confirms acute infection; if positive, termination of pregnancy is offered in many countries, though the decision is ultimately maternal. In India, counseling and supportive care are standard approaches. **High-Yield:** First trimester (especially < 12 weeks) = highest CRS risk. This is tested frequently in PSM and obstetrics. [cite:Park 26e Ch 7]