Complications arise more frequently during the first trimester than at any other stage of pregnancy. Most present with bleeding, pain, or both. Vaginal bleeding occurs in about 20% of clinically diagnosed pregnancies. It causes considerable anxiety for the woman and her partner. In the vast majority of cases, no intervention alters the outcome. The main aim of clinical management is a prompt and accurate diagnosis, with reassurance if the pregnancy is appropriately developed and viable, or appropriate intervention if not. This chapter focuses on the principles of diagnosis and management and three principal diagnoses: miscarriage, ectopic pregnancy, and gestational trophoblastic disease. The other differential diagnoses are shown in Table 5.1.