endometritis, which may occur after a miscarriage (spontaneous abortion) or a delivery, or may be related to a sexually-transmitted infection of the uterus, fallopian tubes or pelvis generally termed pelvic inflammatory disease (PID). Other endometrial causes of abnormal bleeding may relate to the ways that the endometrium heals itself or develops blood vessels. Iatrogenic (caused by medical treatment or procedures): The most common Iatrogenic cause of abnormal bleeding relates to treatment with hormonal medications such as birth control pills, patches, rings, injections, implants, and intrauterine devices (IUDs). Hormone therapy for treatment of menopausal symptoms can also cause abnormal bleeding. Unscheduled bleeding that occurs during such hormonal treatment is termed "breakthrough bleeding" (BTB) Breakthrough bleeding may result from inconsistent use of hormonal treatment, although in the initial months after initiation of a method, it may occur even with perfect use, and may ultimately affect adherence to the medication regimen. The risk of breakthrough bleeding with oral contraceptives is greater if pills are missed. Not classified: The Not Classified category of the PALM-COEIN system includes conditions that may be rare, or whose contribution to abnormal bleeding has not been well established or understood. Pregnancy Vaginal bleeding occurs during 15–25% of first trimester pregnancies. Of these, half go on to miscarry and half bring the fetus to term. There are a number of causes including complications to the placenta, such as placental abruption and placenta previa. Other causes include miscarriage, ectopic pregnancy, molar pregnancy, incompetent cervix, uterine rupture, and preterm labor. Bleeding in early pregnancy may be a sign of a threatened or incomplete miscarriage. In the second or third trimester a placenta previa (a placenta partially or completely overlying the cervix) may bleed quite severely. Placental abruption is often associated with uterine bleeding as well as uterine pain. Postmenopausal Endometrial atrophy, uterine fibroids, and endometrial cancer are common causes of postmenopausal vaginal bleeding. About 10% of cases are due to endometrial cancer. Uterine fibroids are benign tumors made of muscle cells and other tissues located in and around the wall of the uterus. Women with fibroids do not always have symptoms, but some experience vaginal bleeding between periods, pain during sex, and lower back pain. Diagnostic evaluation The cause of the bleeding can often be discerned on the basis of the bleeding history, physical examination, and other medical tests as appropriate. The physical examination for evaluating vaginal bleeding typically includes visualization of