Syphilis in pregnancy is a curable bacterial infection (Treponema pallidum) that can pass to the baby and cause miscarriage, stillbirth, or lifelong disability. Universal blood screening early in pregnancy and a penicillin injection prevent that. The USPSTF gives early screening a Grade A recommendation for every pregnant person USPSTF.
| Item | Reported cases (babies) |
|---|---|
| 2020 | 2,163 |
| 2021 | 2,881 |
| 2022 | 3,769 |
| 2023 | 3,882 |
What syphilis in pregnancy actually is
Syphilis is caused by the bacterium Treponema pallidum and is curable with the right antibiotics CDC. In pregnancy the bacteria cross the placenta and infect the fetus, causing congenital syphilis. Prenatal screening plus penicillin prevents that, yet US cases are surging: congenital syphilis nearly doubled from 2,163 cases in 2020 to 3,882 in 2023, a 77% rise and its highest level in decades CDC. We cover the newborn side in depth on syphilis in pregnancy & congenital syphilis.
Symptoms — and the silent reality
Syphilis moves through stages, and it feels like it's resolving on its own. The primary stage brings one or more painless, firm, round sores (chancres) at the site of infection — the genitals, anus, rectum, lips, or mouth — appearing about three weeks after exposure. A chancre lasts 3 to 6 weeks and heals whether or not you're treated.
The secondary stage can bring a rough red or reddish-brown rash, often on the palms and soles, plus fever, swollen lymph nodes, sore throat, patchy hair loss, headache, weight loss, muscle aches, and fatigue. These symptoms also fade on their own, but fading is not curing. Without treatment the infection moves into a latent stage with no symptoms at all, where it persists for years and is detectable only by blood test. In pregnancy the painless first sore is often hidden; it heals while the infection moves inward and you feel fine.
Syphilis can invade the eyes or nervous system at any stage; ocular syphilis and neurosyphilis are not just late complications. New vision changes or neurological symptoms in someone with syphilis are a medical emergency. Don't watch and wait.
How it spreads
Syphilis spreads by direct contact with a sore during vaginal, anal, or oral sex, and from parent to baby during pregnancy. Because the chancre can sit somewhere you can't see it, transmission often happens before anyone knows there's an infection. Having syphilis also roughly doubles the risk of acquiring HIV.
How syphilis is tested in pregnancy
Testing is a simple blood draw, but a diagnosis needs two serologic tests: a nontreponemal test (RPR or VDRL) and a treponemal test (TP-PA, FTA-ABS, EIA, or CIA) CDC labs, 2024. Either order works — traditional (nontreponemal first, confirm with treponemal) or reverse-sequence (treponemal first, then a quantitative nontreponemal). The mechanics are the same as a standard syphilis test.
Serologic tests can be nonreactive in the earliest infection. Antibodies may take up to two weeks to show after the chancre appears, and the chancre itself shows around three weeks after exposure. If an early test is negative but the risk was recent, retest rather than trusting that negative — see when to test after exposure for timing.
For pregnancy, the USPSTF recommends early, universal screening for everyone, regardless of risk. If someone isn't screened early, screen at the first opportunity, even at delivery. Many states require testing at multiple points in pregnancy. You can get tested confidentially, and if you want to weigh options, you can compare testing providers.
Treatment: penicillin is the only safe option in pregnancy
Penicillin G, given as an injection, is the preferred drug for every stage of syphilis CDC Tx Guidelines. The dose follows the stage: primary, secondary, and early latent syphilis is treated with benzathine penicillin G 2.4 million units IM in a single dose. Late latent or unknown-duration syphilis needs 7.2 million units total — three doses of 2.4 million units IM at one-week intervals. No oral drug dependably substitutes. Full regimens, including neurosyphilis dosing, live on our syphilis treatment page.
The correct drug is benzathine penicillin G (Bicillin L-A). The combination product Bicillin C-R is not an acceptable substitute and has caused treatment-failure errors.
Pregnancy is the one setting with no alternative. Pregnant patients with syphilis at any stage who report penicillin allergy should be desensitized and treated with penicillin, because nothing else reliably protects the baby. Most penicillin allergy is mislabeled anyway — over 90% of people who think they're allergic are not. Outside pregnancy, doxycycline 100 mg twice daily can substitute (14 days for early disease, 28 days for late latent); azithromycin is not recommended because of resistance CDC.
A short reaction usually follows the first shot. The Jarisch-Herxheimer reaction — fever, chills, headache, and muscle aches within the first 24 hours — affects roughly 95% of people treated for secondary syphilis and settles within about a day. It's dying bacteria releasing inflammatory signals, not a penicillin allergy StatPearls.
Cure is confirmed by blood titers, not by feeling better. Repeat quantitative RPR/VDRL at 6 and 12 months for primary/secondary disease (and 6, 12, and 24 months for latent). A fourfold drop — say 1:32 to 1:8 — confirms the treatment worked; a fourfold rise signals reinfection or failure.
What untreated syphilis does to a pregnancy
Untreated syphilis in pregnancy harms the baby in 50 to 80% of cases. The possible outcomes are severe and concrete:
- Miscarriage, stillbirth, or newborn death — the infection can end a pregnancy.
- Prematurity and low birth weight, raising the risk of complications at birth.
- Deformed bones and anemia (a shortage of healthy red blood cells, which carry oxygen).
- Brain and nerve damage, including blindness and deafness that can be permanent.
In the untreated parent, syphilis can progress to a tertiary stage 10 to 30 years later (sometimes sooner), damaging the heart, blood vessels, brain, and nervous system, and it can be fatal. Neurosyphilis and ocular syphilis can occur at any stage StatPearls.
How treatment maps to stage
| Stage | Definition | Penicillin regimen |
|---|---|---|
| Primary / secondary / early latent | Acquired within the past 12 months | Benzathine penicillin G 2.4 million units IM, single dose |
| Late latent / unknown duration / tertiary | More than 1 year, or duration unknown | 2.4 million units IM weekly × 3 (7.2 million total) |
| Neuro / ocular / otosyphilis | CNS or eye involvement, any stage | Aqueous crystalline penicillin G IV, 10–14 days |
The early/late split sets the schedule. Early latent means documented acquisition within the preceding 12 months; otherwise it's treated as late latent or unknown duration CDC.
Prevention
For the parent, the basics still work: correct and consistent condom use, mutual monogamy with a tested-negative partner, and routine screening, which the USPSTF recommends (Grade A, 2022) for nonpregnant adults at increased risk, including men who have sex with men and people with HIV or other STIs USPSTF, 2022. DoxyPEP — 200 mg doxycycline within 72 hours after sex — cut syphilis acquisition by about 73% in trials and is offered via shared decision-making to MSM and transgender women with a bacterial STI in the past 12 months CDC DoxyPEP, 2024.
For the baby, prevention is prenatal screening plus penicillin. There's no separate vaccine or barrier. Catching the parent's infection on a routine blood test and treating it stops congenital syphilis.
When to see a clinician
Start prenatal care early and get the first-trimester syphilis test, even if you feel well, since most infections are silent. See a clinician promptly for a painless genital, anal, or oral sore, or a rash on the palms and soles. Seek emergency care for new vision changes or neurological symptoms if you have or might have syphilis. And if a recent test was negative but the exposure was recent, go back and retest.