This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Contraceptives, Subject name: Gynaecology & Obstetrics
All of the following mechanisms might account for a reduced risk of upper genital tract infection in users of progestin - releasing IUDs, except: 
Select and explain. 
A. Reduced retrograde menstruation, B. Decreased ovulation, C. Thickened cervical mucus, D. Decrease incidence of surgical aboion
B: Decreased ovulation
Answer: B: Decreased ovulation 
Explanation: Reducing ovulation will not have an effect on the incidence of PID. All other factors are helpful in reducing the physical transpo of bacteria like the thick cervical mucus. Decrease incidence of surgical aboions by prevention of unwanted pregnancy Reduction of menstruation with progesterones will eventually also reduce the amount of Retrograde menstruation.