Infection Risk Rises During Menstruation... menstruation is likely to be the time of greatest bacterial contamination (including infection from gonorrhea and chlamydia). This occurs for two reasons.(1) When the mucus barrier in the cervix is lost during menses, the bacteria that live in the cervical canal and vagina may gain access to the uterus and upper genital tract.(2) Through observations in laparoscopy, we know that 90 percent of women with normal, unobstructed Fallopian tubes have retrograde menstruation. That is, menstrual blood and debris are flushed upward into the tubes and pelvic cavity, as well as down into the vagina.This two-directional menstrual flow provides another mechanism for bacteria to pass from the lower genital tract into the Fallopian tubes. This may explain why symptoms of upper genital tract infection often appear shortly after menstruation. ...DAVID A. GRIMES M.D. NANCY S. PADIAN A. EUGENE WASHINGTON, M.D. San Francisco, Sept. 27, 1993 The writers are professors in obstetrics, gynecology and reproductive sciences, University of California.http://www.nytimes.com/1993/10/06/opinion/l-infection-risk-rises-during-menstruation-654193.html