Medications selected to treat problems of pregnancy in the mare must be simultaneously safe for the mare, safe for the developing fetus, and able to penetrate the placental barrier. With consideration of these factors, the practitioner must determine when and for how long to administer therapy. Monitoring equine pregnancy can be challenging, owing to the size of the equine abdomen (precluding visualization of the entire fetoplacental unit), individual variation in appearance of the reproductive tract, and (typically) minimal clinical signs of pregnancy compromise until late in a disease process. This paper is an extension of an article originally prepared for the 2023 Proceedings of the American Association of Equine Practitioners, produced with permission.