Vaccination of pregnant women provides important health benefits to both, mother and infant, and has been an important disease prevention strategy in these two groups. While most vaccines currently licensed in the US are not indicated for use during pregnancy, depending on the vaccine, vaccination programs do frequently include pregnant women. In addition, recent emphasis has been placed on maternal immunization strategies to protect young infants from severe infections. Currently, unless the vaccine is specifically indicated four maternal immunization, no data are collected regarding the vaccine's safety in pregnant women prior to licensure. However, more females of childbearing age participate in clinical trials and a broad range of novel vaccine products are in development indicated for adolescents and adults. Thus, there is increasing concern for the unintentional exposure of an embryo/fetus before information is available regarding the potential risk versus benefit of the vaccine. Since pregnant women are usually excluded from participation in clinical trials, conclusions regarding developmental risk at the time of licensure are frequently based solely on data derived from developmental toxicity studies in animal models. This paper will review regulatory, preclinical and clinical issues as they pertain to development programs for vaccines intended for vaccination during pregnancy.