Which of the following perinatal infections has the highest risk of fetal transmission in the first trimester?

Rubella virus predominant affects the fetus and is extremely teratogenic when infection occur in the first trimester. Risk of major anomalies when rubella occurs in first, second, third month is approximately 50%, 25%, and 10% respectively. CONGENTAL RUBELLA SYNDROME (CRS): Maternal infection with rubella in early gestation interferes with critical organ development in the fetus. The defects resulting from this infection such as cataracts, blindness, deafness, cardiovascular anomalies, microcephaly, and mental retardation are collectively referred to as congenital rubella syndrome (CRS). Ref: Textbook of Obstetrics By D.C.Dutta, 6th Edition, Pages 292-3, 296, 299 ; Text Book of Pediatrics By Nelson, 17th Edition, Page 630.