Bacteria that travel through the urethra to the bladder during intercourse, changes in the urinary tract due to hormones and the use of spermicides and diaphragms often cause bladder infections, according to WebMD. Infections develop when strains of bacteria reach the bladder.
Both men and women can develop bladder infections from sexually transmitted bacteria, such as mycoplasma and chlamydia, explains WebMD. Women who have frequent intercourse are more at risk for a bladder infection because of the exposure to bacteria. With an influx of hormones present in the body and increased function of the kidneys, pregnant women can be more susceptible to bladder infections.