Sexual contact is the primary means by which PID is spread. Untreated sexually transmitted diseases (STDs) such as gonorrhea or chlamydia are believed to be the reason for nearly 90% of PID cases. However, PID may also occur after childbirth, insertion of an IUD, abortion, or pelvic surgery.
PID can cause scarring of the pelvic organs. When scarring occurs in the fallopian tubes, it can lead to an increased risk of ectopic pregnancy.
More in-depth information on pelvic inflammatory disease:
Pelvic Inflammatory Disease: Women's Health
Pelvic Inflammatory Disease: Sexually-Transmitted Diseases