Which one of the following perinatal infections has the highest risk of fetal infection in the first trimester?
**Core Concept**
Toxoplasmosis is a perinatal infection caused by the protozoan parasite *Toxoplasma gondii*. It can be transmitted from mother to fetus, leading to severe congenital anomalies and fetal infection.
**Why the Correct Answer is Right**
The risk of fetal infection in toxoplasmosis is particularly high in the first trimester due to the immaturity of the placental barrier. This allows the parasite to easily cross the placenta and infect the developing fetus. The parasite can cause damage to the fetal brain, eyes, and other organs, leading to congenital toxoplasmosis.
**Why Each Wrong Option is Incorrect**
* **Option A:** Rubella infection is a significant perinatal infection, but its risk of fetal infection is highest in the first 8-12 weeks of gestation, not the first trimester specifically.
* **Option B:** CMV (Cytomegalovirus) infection is a leading cause of congenital viral infection, but its risk of fetal infection is highest in the third trimester.
* **Option D:** Parvovirus B19 infection is associated with fetal anemia and hydrops, but its risk of fetal infection is not as high as toxoplasmosis in the first trimester.
**Clinical Pearl / High-Yield Fact**
Toxoplasmosis can be prevented by avoiding exposure to cat feces, using safe food handling practices, and avoiding undercooked meat.
**Correct Answer:** C. Toxoplasmosis.