Most drugs are not tested for use during pregnancy, consequently, labeling, which may include information about fetal safety, includes nothing about dosing, efficacy, or maternal safety. Yet these are concerns of health care providers considering treatment of disease during pregnancy. Therefore, the practitioner treats the pregnant woman with the same dose recommended for use in adults (typically men) or may decide not to treat the disease at all. However, is the choice of not treating a woman during pregnancy better than dealing with the challenges which accompany treatment? This paper, which summarizes metabolic and physiologic changes induced by pregnancy, illustrates that standard adult dosing is likely to be incorrect during pregnancy.