The diagnosis of pregnancy has traditionally been made based on history and physical examination findings. Important aspects of the menstrual history must be obtained. The woman should describe her usual menstrual pattern, including date of onset of last menses, duration, flow, and frequency. Items that may confuse the diagnosis of early pregnancy are an atypical last menstrual period, contraceptive use, and a history of irregular menses. Additionally, as many as 25% of women bleed during their first trimester, further complicating the assessment