A common sexually transmitted disease, often with no visible symptoms. Left untreated, chlamydia can make a woman infertile. If a woman who has chlamydia becomes pregnant, she can pass the infection on to the baby, causing pneumonia, eye infections, and, in severe cases, blindness. Chlamydia is treatable with antibiotics. All babies receive antibiotics in their eyes after they are born to protect against chlamydia.