This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infectious disease, Subject name: Pediatrics
Non immune hydrops fetalis is caused by 
Select and explain. 
A. HIV, B. CMV, C. HSV, D. Parvovirus B 19
D: Parvovirus B 19
Answer: D: Parvovirus B 19 
Explanation: Primary fetal infection is associated with nonimmune fetal hydrops and intrauterine fetal demise,with the risk for fetal loss after infection estimated at <5%. The mechanism of fetal disease appears to be a viral-induced RBC aplasia at a time when the fetal erythroid fraction is rapidly expanding ,leading to profound anemia, high-output cardiac failure, and fetal hydrops. Nonimmune type * Three major causes -- parvovirus B 19 -- alfa-thalassemia -- cardiovascular defects, chromosomal anomalies, and fetal anemia Reference: Nelson textbook of pediatrics 19th edition, Page 1096