Given that maternal IgM does not cross the placental barrier but can be produced by the fetus in response to intrauterine infections starting at 20–22 GW [10], the presence of rubella IgM in the newborn sera suggests that RA27/3 can cross the placenta with resultant congenital rubella infection (CRI), which can persist from ≤4 GW to at least 20 GW. The gene discussed is CD40LG; the disease is rubella.