This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Veical transmission of toxoplasmosis most commonly occurs during which stage of pregnancy? 
Select and explain. 
A. 1st trimester, B. 2nd trimester, C. 3rd trimester, D. During delivery
C: 3rd trimester
Answer: C: 3rd trimester 
Explanation: Veical transmission of toxoplasmosis is maximum in the third trimester (60%). Risk of fetal transmission of infection during first trimester is 15% and 30% during second trimester. Fetus is at risk of infection only when the mother is seronegative. Affected babies develop hydrocephalus, choroidoretinitis, cerebral calcification, microcephaly and mental retardation. Presence of IgM antinody in neonates indicates congenital infection.