Chlamydia (say "kluh-MID-ee-uh") is one of the most common sexually transmitted infections (STIs). In men, it infects the urethra. In women, it infects the urethra and the cervix. It can also spread to a woman's reproductive organs.

Chlamydia doesn't cause problems if you treat it right away. But if you don't treat it, it can lead to serious problems, especially for women:

• If it spreads, it can cause pelvic inflammatory disease. This serious infection can make it hard or impossible for a woman to get pregnant.
• Pregnant women who have chlamydia often pass it to their babies at birth. If the infection gets in a baby's eyes, it can cause blindness. Babies can also have other problems, like pneumonia. Pneumonia can be deadly in a newborn.