Placental abruption is exactly what it sounds like - abnormal detachment of the placenta from the uterine lining and wall (in a normal pregnancy, the placenta detaches from the uterine wall only after the baby has been delivered - this is called the afterbirth). Its prevalence is estimated to be fairly low at less than 1% of pregnancies. Placental abruption usually occurs in the third trimester, but can occur as early as in the second trimester in some cases. It can be partial (milder) or total (more severe). Symptoms include bleeding (but not necessarily because the blood can be trapped between the placenta and the uterine wall, which is called a concealed abruption), bloating (tenderness), abdominal and back pain, rapid contractions. 

Placental abruption can be caused by a variety of issues, such as trauma (accidents), drug abuse (cocaine), or preexisting chronic conditions (such as hypertensive disorders). Therefore, the only things you can do to reduce your risk of placental abruption is to have a safe and healthy lifestyle (avoid accidents and drug use, eat a healthy diet and stay active).  If you do have a placental abruption, treatment depends on whether the abruption is partial (milder) or total (stronger). Milder partial abruptions can be managed with cautious observation and monitoring either in the hospital or at home (including fetal heart rate monitoring, FHR, to make sure your baby has enough oxygen). If necessary, medical treatments that help the fetus mature (such as corticosteroids for lung maturation) can be given, so that your baby can be delivered preterm if need be. Stronger total abruptions can deprive the fetus of important nutrients and oxygen if left unattended, and can require immediate delivery either by induced labor or c-section. If your baby was delivered preterm due to placental abruption, it may need to stay in an incubator for a few days or even weeks.