Which one of the following viruses is least likely to cross placenta?
Considering all the above given options, the hepatitis B virus is least likely to cross the placenta due to its larger molecular size (virion of 42nm in diameter) which gives it less access through the placenta. It is not teratogenic. Ref: Dutta Textbook of obstetrics 6th edition, Pages 292, 299-300; Medical disorders in pregnancy: an update By Hiralal Konar, Pralhad Kushtagi, Pages 67-74.
Rubella
Herpes Simplex Virus
HIV
HBV