The concern over RhoGAM is based on the fact that in its earlier form it contained thimerosal. Between1968 (when RhoGAM was first licensed) and April of 2001, RhoGAM contained the thimerosal preservative. Thimerosal contains ethylmercury and because methylmercury (another mercury based composition) has been found to cause severe health problems, ethylmercury is also being scrutinized. Both compositions are known to be neurotoxins. To date, no conclusive evidence has been found linking ethylmercury to neurodevelopmental disorders, but the FDA has treated thimerosal with caution.

Oh, the horror! Calm down. Please, it's not that serious...