Untreated chlamydial infections in females can lead to pelvic inflammatory disease (PID), and PID-associated infertility, ectopic pregnancy, and chronic pelvic pain. Untreated chlamydia during pregnancy has been associated with preterm delivery. Chlamydial infections can be passed to newborns during delivery, increasing the risk of conjunctivitis (18-44% of cases) and pneumonia (3-16% of cases).
Complications in untreated males are rare, but can include epididymitis and infertility. Chlamydial infections can also facilitate the transmission of HIV infection, and in rare cases can cause reactive arthritis.