A sexually transmitted infection (STI) is a bacterial or viral illness you can catch from having vaginal, oral, or anal sex with someone who is infected. Your doctor might call this type of infection a sexually transmitted disease (STD). Untreated STIs can cause serious health problems for you and your baby.

You can also get these infections in other ways. For example, the hepatitis B virus spreads through body fluids when people share needles or personal items such as a toothbrush or razor.

Some of the most common STIs that can affect pregnancy include:

• Chlamydia

• Genital herpes

• Gonorrhea

• Hepatitis B (HPB)

• Hepatitis C (HCV)

• HIV/AIDS

• Human papillomavirus (HPV)

• Syphilis

• Trichomoniasis (Trich)

Some infections can pass to your baby while you're pregnant, during labor and delivery, or during breastfeeding. In some cases, these infections can cause serious health problems for babies.

STIs are linked to problems such as:

• Infertility or problems getting pregnant

• Preterm labor

• Poor growth

• Low birth weight

• Stillbirth

• Abnormalities in the baby's organs

• Pneumonia, eye infections, or other infections impacting a baby at birth

Many times, people with STIs don't have visible symptoms. However, if symptoms are present they may include:

• Swelling or redness near the vagina

• Skin rash

• Sores or warts near the mouth, anus, or vagina

• Aches, pains, fever, and/or chills

• Yellowing of the skin (jaundice)

• Vaginal discharge (may have a bad odor) 

• Painful sex

• Vaginal itching

• Weight loss

• Night sweats

Since you may not have any symptoms, the most accurate way to find out if you have an STI is to get tested during pregnancy. Getting treatment quickly if you test positive could improve the outcome for you and your baby.

It's important to have open and honest conversations with your provider: Discuss any symptoms you're experiencing and any high-risk sexual behavior you've engaged in. 

You might be at risk for an STI if:

• You had an STI in the past

• You or your partner has sex with other people

• Your partner has tested positive for an STI

• You've shared needles for injected drugs or tattoos

Even if you're not at high risk now, some STIs can stay in your body for years without causing symptoms. You want to be sure that you or your partner didn't get an infection in the past without knowing it.

The Centers for Disease Control and Prevention (CDC) recommends that every pregnant woman get screened for syphilis, HIV, hepatitis B, and hepatitis C and during the first prenatal visit. The CDC also suggests screening for chlamydia and gonorrhea at your first visit if you're under 25 and/or you have risk factors.

Your doctor might screen you again in your third trimester if you're still at high risk. If you think you might have been exposed to an STI during your pregnancy, or if you or your partner has any unusual symptoms, make sure to tell your doctor right away so you can be retested.

Yes. The treatment depends on the type of STI you have. Antibiotics treat infections caused by bacteria, like chlamydia, gonorrhea, and syphilis. Many antibiotics are safe in pregnancy, including: 

• Beta-lactams, like penicillin and amoxicillin

• Clindamycin

• Metronidazole

• Nitrofurantoin

• Vancomycin

• Cephalosporin

Antibiotics such as fluoroquinolones and tetracyclines are generally not recommended during pregnancy. Your doctor can explain which antibiotic they're prescribing, why it's indicated, and any possible side effects.

Antibiotics don't treat viral infections like herpes, hepatitis, and HIV. But antiviral medicine and other treatments can relieve your symptoms and may reduce your risk of passing the virus to your baby.

If you have genital herpes, your doctor may start antiviral medications in the third trimester to prevent outbreaks and reduce the risk of recurrent infection. Once you start labor, your doctor will ask if you're experiencing any symptoms and look for signs that you're having an outbreak by performing a physical exam. You may need a C-section if you're having an active genital outbreak at the time of delivery to prevent your baby from being exposed to herpes during birth.

If you're HIV-positive, taking a combination of anti-HIV drugs can help you stay as healthy as possible and reduce the risk of your baby getting infected. You may have your baby by C-section if lab tests show that you have a high level of HIV in your body.

It's important for both you and your partner to be treated for an STI. Try to avoid having sex until you've both finished treatment and are symptom-free. Otherwise, you could pass the infection back and forth.

The only sure way to avoid getting an STI is to not have any kind of sex – vaginal, oral, or anal. But that's not a feasible option for many of us. Here are ways to reduce your risk:

• Have sex with only one partner, who only has sex with you. (The fewer partners you both have, the lower the risk.)

• Be sure that you and your partner are tested for STIs. 

• Don't use intravenous drugs, and make sure your partner doesn't either.

• If you or your partner are at risk for STIs, use a latex condom every time you have sex, and a dental dam every time you have oral sex.

• Know the signs and symptoms of STIs, and watch for them in your partner and yourself.

• Get vaccinated against HPV and hepatitis B. The HPV vaccine isn't safe to get when you're pregnant, so get it before pregnancy if possible. The hepatitis B vaccine may be safe during pregnancy, depending on your situation.

Yes, some STIs can pass from you to your baby. Syphilis can cross the placenta to your baby in the womb. Gonorrhea, chlamydia, hepatitis B, HIV, and herpes can pass to your baby during labor.

Babies who are infected in the womb can be born with HIV, herpes, or syphilis. Getting tested for STIs and treated during your pregnancy can help prevent you from passing one of these infections to your baby.