Although premature separation of normally implanted placenta is considered the most serious complication of pregnancy, knowledge of uterine behaviour during this con­dition is meager, on the basis of electronic recording of intra-uterine pressure two type of contraction pattern has been identified. 
In type I uterine tonus has values below 30mmHg 
with a frequency of 4-9 contractions per 10 minutes. 
In type II uterine tonus has a value of 30 mm Hg or more and a higher frequency. 
Cases falling in type I react to the administration of oxytocin, while those in type II do not. 
So uterine tonus and contraction frequency appear to be a good indicator of the functional status of uterine mmcle in abruptic placenta and its reactivity to oxytocic agents.