This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abnormal labor, Subject name: Anatomy
[{'content': 'Traction force required for forceps delivery in primigravida is : \nSelect and explain. \nA. 15 kgs, B. 18-20 kgs, C. 13 kgs, D. 25 kgs', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Traction force required by forceps is: Primigravida -18-20 kgs Multigravida-13 kgs Vacuum - initial pressure is 0.2 kg/cm2 induced over 2 minutes. The pressure is gradually increased at the rate of 0.1 kg/cm2 to a maximum of 0.8 kg/cm2. Ref: Datta Obs 9e pg 533.', 'role': 'assistant'}]