Congenital rubella syndrome is most prominent in an infant when a pregnant woman becomes infected?

The route of infection of rubella virus is the respiratory tract, with spread to lymphatic tissue and then to the blood (viremia). Maternal viremia is followed by infection of the placenta, which leads to congenital rubella. Many organs of the fetus suppo the multiplication of the virus, which does not seem to destroy the cells but reduces the rate of growth of the infected cells. This leads to fewer than normal numbers of cells in the organs at bih. Therefore, the earlier in pregnancy infection occurs, the greater the chance for the development of abnormalities in the infected fetus. A vast percentage of maternal infections that occur during the first trimester of pregnancy result in such fetal defects as pulmonary stenosis, ventricular septal defect, cataracts, glaucoma, deafness, mental retardation, and other maladies. Ref: Brooks G.F. (2013). Chapter 40. Paramyxoviruses and Rubella Virus. In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.