The diagnosis is one of exclusion, meaning other possible sources of vaginal bleeding or abdominal pain have to be ruled out in order to diagnose placental abruption. Of note, use of magnetic resonance imaging has been found to be highly sensitive in depicting placental abruption, and may be considered if no ultrasound evidence of placental abruption is present, especially if the diagnosis of placental abruption would change management. Classification
Based on severity:

Class 0: Asymptomatic. Diagnosis is made retrospectively by finding an organized blood clot or a depressed area on a delivered placenta. Class 1: Mild and represents approximately 48% of all cases. Characteristics include the following:
No vaginal bleeding to mild vaginal bleeding
Slightly tender uterus
Normal maternal blood pressure and heart rate
No coagulopathy
No fetal distress
Class 2: Moderate and represents approximately 27% of all cases. Characteristics include the following:
No vaginal bleeding to moderate vaginal bleeding
Moderate-to-severe uterine tenderness with possible tetanic contractions
Maternal tachycardia with orthostatic changes in blood pressure and heart rate
Fetal distress
Hypofibrinogenemia (i.e., 50–250 mg/dL)
Class 3: Severe and represents approximately 24% of all cases. Characteristics include the following:
No vaginal bleeding to heavy vaginal bleeding
Very painful tetanic uterus
Maternal shock
Hypofibrinogenemia (i.e., <150 mg/dL)
Coagulopathy
Fetal death

Prevention
Although the risk of placental abruption cannot be eliminated, it can be reduced. Avoiding tobacco, alcohol and cocaine during pregnancy decreases the risk. Staying away from activities which have a high risk of physical trauma is also important.
Though different causes change when abruption is most likely to occur, the majority of placental abruptions occur before 37 weeks gestation, and 12–14% occur before 32 weeks gestation. == References ==