These protective mechanisms, however, may be overcome or impaired in certain circumstances. For example, when women engage in sexual intercourse, there is often substantial displacement of both fecal and vaginal fora toward the urethra. This risk further increases with the use of diaphragms or spermicides, which may render the vaginal environment more hospitable to the proliferation of uropathogens. In older women, a decline in estrogen can lead to a loss of the protective lactobacilli that are part of the normal vaginal fora, enabling increased colonization with uropathogens. Pregnancy alters the pH and osmolality of urine, making it more favorable to bacterial growth.