STI Testing During Pregnancy — What to Expect and Why

If you're pregnant in the United States, you'll be tested for several STIs as part of routine prenatal care. This isn't optional or extra — it's standard, recommended by ACOG and CDC, and the stakes for the baby are real.

Here's what gets tested, when, and what happens if any of them come back positive.

The short answer

Standard prenatal STI screening includes:

Note: Group B Strep isn't an STI but is tested in late pregnancy because of newborn risk.

Why STIs matter in pregnancy

STIs in pregnancy can affect:

• The mother: Complications during pregnancy and delivery
• The pregnancy: Preterm labor, premature rupture of membranes, low birth weight
• The newborn: Direct infection (vertical transmission) during pregnancy, delivery, or breastfeeding

Most STIs are highly treatable in pregnancy. Untreated STIs cause more harm than the treatments themselves.

Each test, by STI

HIV

• Why: Without treatment, mother-to-child HIV transmission is 15-45%. With treatment, < 1%.
• When: First prenatal visit; opt-out (you can decline, but it's offered routinely). Repeat third trimester if high-risk.
• If positive: Antiretroviral therapy (ART) throughout pregnancy. Cesarean if high viral load near delivery. No breastfeeding (formula recommended in US). Newborn gets prophylactic ART.
• Outcome: Babies of HIV+ mothers on consistent ART have < 1% chance of HIV.

Syphilis

• Why: Congenital syphilis can cause stillbirth, neonatal death, deafness, blindness, bone deformities. US cases have risen sharply since 2017.
• When: First visit; repeat 28 weeks AND at delivery in high-prevalence areas or for high-risk women
• If positive: Penicillin (the only effective treatment). Penicillin allergic → desensitization required (doxycycline alternatives are NOT safe in pregnancy)
• Outcome: Treated maternal syphilis before 24 weeks is nearly 100% effective at preventing congenital syphilis. Later treatment still helps.

Hepatitis B (HBV)

• Why: Without intervention, 90% of newborns infected at birth develop chronic HBV (with serious long-term consequences). With intervention, < 1%.
• When: First prenatal visit
• If positive: Antiviral medication in third trimester if high viral load. At birth: baby gets HBIG + HBV vaccine within 12 hours.
• Outcome: Combined intervention prevents almost all transmission.

Hepatitis C (HCV)

• Why: 5-15% transmission rate to baby. No HCV vaccine. No pre-delivery treatment proven safe in pregnancy.
• When: First prenatal visit (universal screening since 2020)
• If positive: No treatment in pregnancy. Baby tested at 18 months. Many babies clear infection spontaneously.

Chlamydia

• Why: Can cause conjunctivitis or pneumonia in newborn. Also linked to preterm birth and low birth weight.
• When: First visit if under 25 or risk factors. Repeat third trimester if high-risk.
• If positive: Azithromycin 1g single dose (doxycycline is NOT used in pregnancy). Repeat test at 3-4 weeks.
• Outcome: Highly treatable in pregnancy.

Gonorrhea

• Why: Can cause neonatal conjunctivitis (potentially leading to blindness), sepsis, joint infections, and preterm labor.
• When: First visit if under 25 or risk factors. Repeat third trimester if high-risk.
• If positive: Ceftriaxone IM + azithromycin. All babies in the US receive prophylactic erythromycin eye ointment at birth as a backstop.
• Outcome: Treated maternal infection prevents most neonatal complications.

Trichomoniasis

• Why: Associated with preterm birth, low birth weight.
• When: Tested if symptomatic
• If positive: Single dose metronidazole 2g, or 500mg twice daily for 7 days (safe in pregnancy after first trimester)

Bacterial vaginosis (BV)

• Why: Increased risk of preterm labor; treatment may reduce it in symptomatic women.
• When: Treated if symptomatic. Routine screening not universally recommended.
• If positive: Oral or vaginal metronidazole, or clindamycin

Herpes (HSV)

• Why: Neonatal herpes is rare but devastating when it occurs (~50% mortality without treatment). Highest risk is maternal NEW infection in third trimester.
• When: No routine blood screening — too many false positives, low utility. But active lesions matter at delivery.
• If positive history: Suppressive antiviral (acyclovir or valacyclovir) from 36 weeks until delivery
• If new infection in third trimester or active lesion at delivery: Cesarean delivery recommended

See herpes and pregnancy for details.

Group B Streptococcus (GBS)

• Why: Not strictly an STI but causes serious newborn infection if untreated. Carried in vagina/rectum in 20-25% of pregnant women.
• When: 36-37 weeks (vaginal/rectal swab)
• If positive: IV antibiotics (penicillin or alternative) during labor
• Outcome: Prevents most early-onset neonatal GBS disease

Why opt-out HIV testing matters

In most US states, HIV testing is offered "opt-out" — meaning it's automatic unless you specifically refuse. This was a major public health win because:

• Reduces stigma (everyone's tested, not just "high-risk")
• Catches HIV in women who don't see themselves as at-risk
• Prevents nearly all mother-to-baby HIV transmission when detected

If your provider asks if you want HIV testing — say yes. The downside of testing is essentially zero. The downside of not testing if positive is enormous.

What if I test positive for something?

The right response depends on the STI, but the principles are:

1. Don't panic

Most STIs are treatable in pregnancy. The vast majority of women with STIs in pregnancy have healthy babies when treated.

2. Treatment is tailored

• Some standard STI drugs (e.g., doxycycline) aren't safe in pregnancy — alternatives exist
• Your provider will pick the right regimen

3. Partner must be treated

• Untreated partners → reinfection → repeat cycle

4. Follow-up is essential

• Re-testing to confirm cure
• Sometimes additional testing or fetal monitoring

5. Tell the pediatrician

• The baby's care team needs to know maternal STI status to plan newborn care correctly

What to ask your prenatal provider

"What STIs am I being tested for? When?"

"Are you doing the full panel or just HIV and syphilis?"

"Should I be tested for HSV — given my history with [X]?"

"If anything is positive, how does treatment work in pregnancy?"

"What happens at delivery if I have an active outbreak / positive test?"

Special situations

Repeat exposures during pregnancy

If you have unprotected sex with a new partner during pregnancy, ask for repeat testing. Routine third-trimester repeat is only done for high-risk pregnancies in many practices.

Coexisting conditions

• HIV + pregnancy → maternal-fetal medicine specialist
• Untreated syphilis + pregnancy → urgent treatment, neonatal infectious disease referral
• Active genital HSV lesions at delivery → cesarean
• HBV + pregnancy → consider antiviral in third trimester

Sexual assault during pregnancy

• Emergency care: STI testing + prophylaxis (HIV PEP, ceftriaxone + azithromycin, etc.)
• Trauma-informed support
• Connect to rape crisis center

Pregnancy after STI exposure

If you had a known exposure before pregnancy:

• Disclose to prenatal provider
• Repeat full STI panel even if recently tested
• Discuss any additional testing or monitoring

The big picture

Modern prenatal care catches most STIs early enough to treat. The system is set up to make sure no baby is born with a preventable STI infection. Comply with testing. Tell your provider about exposures. Take treatments offered.

For most women, this entire process is just a few blood draws and swabs — and a lifetime of healthier outcomes for their babies.

Bottom line

Every pregnancy in the US gets STI screening:

• HIV, syphilis, hepatitis B, hepatitis C, chlamydia, gonorrhea at first prenatal visit
• Repeat syphilis and HIV in third trimester for higher-risk situations
• HSV management based on history and active lesions
• Group B Strep at 36-37 weeks

If positive, treatment is available and safe for most STIs in pregnancy. The cost of not testing is far higher than the cost of testing. Take the screening seriously.

For more, see free STI testing, herpes and pregnancy, hepatitis B vaccine schedule, and STI testing window periods.