The management of patients presenting to the emergency department (ED) with vaginal bleeding depends upon a number of factors including patient age, pregnancy status, chronicity and severity of bleeding, comorbidities, and medications. An understanding of the menstrual cycle and an organized approach to patient evaluation enable the ED clinician to form an appropriate differential diagnosis and treatment plan.
This topic review will discuss the basic physiology of menstruation and provide a basic approach to the adult patient who presents to the ED with vaginal bleeding. Detailed discussions of pediatric patients with vaginal bleeding and of specific causes of genital tract bleeding are found elsewhere. (See "Clinical manifestations and diagnosis of ectopic pregnancy" and "Spontaneous abortion: Risk factors, etiology, clinical manifestations, and diagnostic evaluation" and "Placental abruption: Clinical features and diagnosis" and "Differential diagnosis of genital tract bleeding in women" and "Evaluation and management of lower genital tract trauma in women" and "Approach to abnormal uterine bleeding in nonpregnant reproductive-age women".)
The average age of menarche is approximately 12.5 years. The regularity of the menstrual cycle and ovulation are dependent on a complex hormonal feedback mechanism involving the hypothalamus, the pituitary, and the ovary (figure 1). A basic summary of menstruation follows. A more detailed description of menstruation is found elsewhere. (See "Physiology of the normal menstrual cycle" and "Normal puberty".)
In the follicular phase of the menstrual cycle, gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus which then stimulates the pituitary to release both luteinizing hormone (LH) and follicle stimulating hormone (FSH). In the ovary, under the influence of these two hormones, two things occur: a dominant follicle matures and increasing levels of estrogen are secreted. Once estrogen levels reach a threshold level for about 36 hours, a surge in LH occurs, which triggers ovulation and the beginning of the luteal phase of the menstrual cycle. Under the influence of LH, the ruptured dominant follicle rapidly evolves into the corpus luteum, which secretes increased amounts of progesterone. If pregnancy does not occur, the corpus luteum involutes 14 days after ovulation, progesterone levels fall, and menstruation occurs.
The endometrium is composed of three layers: basal, spongy, and compact. The basal layer contains stem cells for regeneration but also provides a cleavage plane between the basal and spongy layers when menstruation occurs. The endometrium undergoes characteristic changes in structure and thickness during the course of each menstrual cycle.