<prompt> All of the following mechanisms might account for a reduced risk of upper genital tract infection in users of progestin - releasing IUDs, except:Reduced retrograde menstruationDecreased ovulationThickened cervical mucusDecrease incidence of surgical aboion  <response>: 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. 