Sexually transmitted infections (STIs) are infections that spread through sexual contact. STIs can also be called sexually transmitted diseases (STDs).

You can get an STI if you have sexual contact with someone who has an STI. Any sex that involves the penis, vagina, anus, or mouth can spread these infections. Some STIs also spread through body fluids, such as semen, vaginal fluid, blood, or breast milk. Others spread through contact with infected skin.

STIs can be caused by bacteria or viruses. The most common ones include:

• HIV. It comes from a virus that destroys the body's ability to fight infection. It can be passed to your baby during pregnancy or birth or while breastfeeding.
• Genital warts (human papillomavirus, or HPV). This virus can spread inside or outside the genitals or to the surrounding skin. If there are a large number of genital warts, the growths can complicate a vaginal delivery.
• Chlamydia. It's caused by a bacterium. The infection can be passed to your baby at birth.
• Gonorrhea. This can cause infertility or problems during pregnancy, including tubal pregnancy. It can spread to your baby during birth.
• Genital herpes. It comes from the herpes simplex virus (HSV). It can spread to a baby during birth and cause severe infection.
• Syphilis. This bacterial infection can cause dangerous problems for a baby during pregnancy.

STIs can cross the placenta during pregnancy, spread to the baby during a vaginal delivery, or spread through breast milk.

Problems that can happen during pregnancy include:

• Premature labor.
• Complications for vaginal delivery that may require a C-section.
• Miscarriage or stillbirth.
• Infection in the uterus after birth.

These infections can also affect the baby after birth. They can cause:

• Low birth weight.
• Eye infection.
• Brain damage.
• Blindness.
• Deafness.
• Other types of infection, including pneumonia or blood infection.

Screening is often done for those who are considered at higher risk for STIs. Screening can happen throughout pregnancy. You may be retested again later in pregnancy.

Everyone is screened for syphilis during the third trimester of pregnancy and again at birth.

You may also be screened for these STIs during pregnancy:

• HIV.
• Hepatitis B.
• Chlamydia.
• Gonorrhea.

Most STIs have no signs or symptoms. The best way to know if you have an STI is to get tested. But you can also be alert to any changes in your body or your partner's body. Symptoms may appear in, on, or near the vagina, penis, rectum, mouth, or throat. They may include:

• Unusual discharge.
• Lumps, bumps, or rashes.
• Sores that may be painful, itchy, or painless.
• Itchy skin.
• Burning with urination.
• Pain in the pelvis, belly (abdomen), or rectum.
• Bleeding from the rectum.

STIs can be diagnosed at your doctor's office with a:

• Pelvic and physical exam.
• Blood test.
• Urine test.
• Fluid or tissue sample.

Treatment depends on the type of STI. If the infection is from a bacterium, it can often be treated with antibiotics. If the infection is from a virus, it can often be treated with antiviral medicine.

The best way to prevent them is to not have sex. You can lower your risk for STIs when you do have sex by trying to:

• Use an external (male) latex condom or internal (female) polyurethane condom and spermicide.
• Limit the number of sexual partners you have.
• Stay up-to-date on vaccines.
• Talk to your sexual partners about your STI history and testing status, as well as theirs.
• Have regular checkups for HIV and other STIs.
• Learn the symptoms of STIs and seek medical help if symptoms occur.
• Avoid douching.