Blunt injury during pregnancy can cause miscarriages, especially if it occurs after the first trimester of the pregnancy. The most common mechanisms of injury are motor vehicle crashes, falls, and assaults. The effects of traumatic injuries on the pregnancy largely depends on the gestational age of the fetus, as well as the type and the severity of the trauma. In the beginning of pregnancy, the uterus is protected by the pelvis, so a miscarriage caused by blunt trauma to the abdomen is unlikely. If, however, the pregnancy is in its second or third trimester, the outcomes can be more severe. At this point, the uterus begins to expand above the pelvis, and the placenta has fully formed. If there is rapid deceleration, acceleration, or direct injury to the pregnant abdomen during this period, the placenta can detach from the uterus. Such placental abruption, or detachment of the placenta, is associated with complications, such as loss of blood from both the birth parent and fetus, uterine rupture, and miscarriage. Diagnostic ultrasound imaging and fetal heart rate monitoring may be used in emergency medical situations to determine the extent of injury.