Some viruses cause only minor illnesses in children or healthy adults.
But they can be devastating to a fetus. When Jennifer Bailey of Houston was seven months pregnant in 1990, she gained a worrisome amount of weight. Ultrasound revealed that the baby's abdomen was filled with fluid and severely bloated. CMV, also a member of the herpes family, is in saliva and other bodily fluids, and is readily passed among family members or toddlers playing together. Infection usually produces nothing more serious than a cold.