"C. trachomatis" naturally lives only inside human cells. Chlamydia can be transmitted during vaginal, anal, or oral sex. It can also be passed from an infected mother to her baby during vaginal childbirth. Many people with Chlamydia show no symptoms of infection. Between half and three-quarters of all women who have chlamydia have no symptoms and do not know that they are infected. Untreated, chlamydial infections can cause serious reproductive and other health problems with both short-term and long-term consequences.