Syphilis in Pregnancy & Congenital Syphilis

Syphilis in pregnancy is a curable bacterial infection that can pass to the baby and cause miscarriage, stillbirth, or lifelong disability — known as congenital syphilis. The fix is straightforward: every pregnant person should be screened early, and anyone who tests positive needs penicillin, the only treatment proven to protect the fetus.

Why syphilis matters so much in pregnancy

Syphilis is caused by the bacterium Treponema pallidum, and untreated it moves silently through stages — a painless sore, then a body rash, then years with no symptoms at all CDC. That silence is the danger in pregnancy. A parent can feel completely well while the bacteria cross the placenta and infect the developing baby. Because the infection so often hides, screening — not symptoms — is what catches it in time.

The numbers explain the alarm. National syphilis cases keep climbing, with about 53,000 primary-and-secondary cases reported in 2023 CDC AtlasPlus, 2023. Congenital syphilis has followed: cases nearly doubled in four years, from 2,163 in 2020 to 3,882 in 2023 — a 77% rise and the highest level in decades CDC. Preliminary figures show nearly 4,000 cases in 2024, the most since 1994. Almost all of it is preventable with timely screening plus penicillin.

If you're not sure whether your stage matters, it doesn't: penicillin works at every stage, and the baby is at risk at every stage. You can read more about how the infection progresses in our guide to nothingsyphilis symptoms by stage.

Risks to the baby (congenital syphilis)

Untreated syphilis in pregnancy harms the baby in 50 to 80% of cases — a sobering range that includes the worst outcomes WHO. The bacteria reach the fetus through the placenta and, later, through contact with sores at delivery.

What congenital syphilis can do:

• Miscarriage or stillbirth — loss of the pregnancy, which is among the most common severe outcomes.
• Neonatal death — death of the newborn in the days or weeks after birth.
• Prematurity and low birth weight — being born too early or too small, which carries its own risks.
• Bone deformities — abnormal bone development the infection causes during growth.
• Anemia — a low red-blood-cell count that leaves the baby weak and at risk.
• Brain and nerve damage — including blindness and deafness that can be permanent.

Many infected newborns look healthy at birth and only develop problems weeks to years later, which is why diagnosis can't wait for symptoms. Syphilis also roughly doubles the chance of catching HIV, so a positive test should prompt full STI screening for the parent.

When is syphilis screening done in pregnancy?

The U.S. Preventive Services Task Force gives prenatal syphilis screening a Grade A recommendation — its strongest — and recommends early, universal screening for all pregnant people regardless of perceived risk USPSTF, Grade A. "Universal" is deliberate: many parents who deliver a baby with congenital syphilis had no obvious risk factor.

In practice, screening happens at several points:

• At the first prenatal visit — every pregnant person, ideally in the first trimester.
• In the third trimester and again at delivery for those at higher risk or living in high-prevalence areas, since infection can be acquired after the first test.
• At the first opportunity if prenatal care started late — the USPSTF is explicit that someone who wasn't screened early should be screened whenever they're first seen, even at delivery.

Syphilis is far from evenly spread, which is why some regions retest more aggressively. In 2023 the highest primary-and-secondary rates were in South Dakota (73 per 100,000), Washington DC (40), New Mexico (37), and Mississippi (30) — several times the national average. Screening is a two-part blood draw (a nontreponemal test like RPR plus a confirmatory treponemal test); the mechanics are covered in our explainer on the syphilis test. If you had a possible exposure before pregnancy, see when to test after exposure so you understand the window period.

Safe treatment in pregnancy: penicillin only

Penicillin G, given by injection, is the preferred drug for every stage of syphilis — and in pregnancy it's the only treatment proven to cross the placenta and treat the fetus CDC STI Tx Guidelines. No oral antibiotic dependably substitutes.

The schedule follows the stage of infection:

A critical safety point: the correct early-stage product is benzathine penicillin G (Bicillin L-A). The combination product Bicillin C-R is not an acceptable substitute and has caused real treatment-failure errors — a difference worth confirming with whoever gives the shot.

What about penicillin allergy? Most of it is mislabeled — over 90% of people who believe they're allergic actually aren't. The non-pregnant alternatives (doxycycline, for example) are off the table in pregnancy because they don't protect the baby and some can harm the fetus. So a pregnant person with a true penicillin allergy is desensitized — given tiny, escalating doses under medical supervision until they tolerate the drug — and then treated with penicillin anyway. There is no safe alternative. Full regimens, including allergy management, live in our syphilis treatment guide.

Expect a flu-like reaction in the first day. The Jarisch-Herxheimer reaction — fever, chills, headache, and muscle aches within roughly the first 24 hours — happens when dying bacteria release inflammatory signals. It affects roughly 95% of people treated for secondary syphilis and settles within about a day StatPearls. It is not a penicillin allergy. In late pregnancy it can briefly trigger contractions or reduced fetal movement, so it's treated where the baby can be monitored — but it should never be a reason to skip or stop treatment.

Cure is confirmed by blood titers, not by feeling better. Quantitative RPR/VDRL titers are repeated over the following months, and a fourfold drop (for instance, from 1:32 to 1:8) confirms the treatment worked. In pregnancy these are followed closely, and the baby is evaluated and often treated at birth depending on the mother's response and timing.

Reducing transmission around delivery

Treating the parent early in pregnancy is by far the most effective protection — adequate treatment well before delivery dramatically lowers the chance the baby is infected. Beyond that:

• Treat partners — a partner who isn't treated can reinfect you, restarting the risk to the baby.
• Use condoms during pregnancy if there's any ongoing exposure risk; combined with regular screening, this cuts transmission in at-risk couples.
• Avoid contact with active sores, which are highly infectious during the primary and secondary stages.
• Plan newborn evaluation — every baby born to a parent treated for syphilis is examined and tested, and treated with penicillin if there's any uncertainty about adequate prenatal treatment.

Because reinfection is possible, finishing treatment isn't the end — symptoms resolving never means cured on its own. The titer follow-up is what proves it.

When to see a clinician

Get medical care promptly if you're pregnant and any of these apply:

• You haven't been screened for syphilis this pregnancy — ask for it at your next visit; it's standard and recommended for everyone.
• You or a partner has a painless sore, an unexplained rash (especially on the palms or soles), or a recent positive test.
• You develop new vision changes or neurological symptoms — syphilis can invade the eyes or nervous system at any stage, and that's a medical emergency.
• You were treated but your titers aren't falling, or a partner wasn't treated.

If you've never been tested or it's been a while, you can get tested — for pregnancy, do it as early as possible.