Emerging infections and pregnancy: assessing the impact on the embryo or fetus

The teratogenicity of several infections when acquired during pregnancy is well documented. However, for emerging infections (defined as those for which the incidence has risen in the past two decades or threatens to rise in the near future), the prenatal effects are often unknown, raising concern among women and their health care providers. Investigation of these effects is essential to ensure that pregnant women are appropriately assessed, advised, and treated, but such investigation is often challenging. The impact of emerging infections on the embryo or fetus is difficult to predict and varies depending on the agent and gestational timing of infection. Some women might be asymptomatic or have only mild or nonspecific symptoms, and thus, not be identified as infected, even when the embryo or fetus is severely affected. In addition, diagnosing congenital infection is often complicated. This article will discuss challenges to studying the teratogenicity of emerging infections, advantages, and disadvantages of different study designs, and examples of previous studies of the effects of emerging infections on the embryo or fetus.