Your cervix and your uterus are not sterile
Like the mouth, the vagina, the rectum, the bladder, the uterus is not a sterile place. Although the original "recent" work was many years ago by a Dr. Bartlett (1977) they showed on average there were at least 2.1 species of bacteria living in the uterus at all times. and 4.2 "at the gate" in the cervix. More recently there was a study published that reviewed what we know so far, and concluded much work needs to be done. So the conclusion is the same, the uterus and the cervix are not a sterile place at all and there are ways that bacteria make it past that normal cervical mucus barrier to get more internally to the uterus. We do know there is a pump that can move particles, like sperm, up past that mucus barrier. And we do know the IUD to some extent may have the protruding strings disrupt the barrier.. The more we think about it, the more questions scientist propose! What the "function" of the bacteria living there are is of yet unknown, but I'd loved to hear your thoughts!