Congenital Syphilis: Prenatal Screening and Newborn Treatment

Congenital syphilis is the most preventable tragedy in obstetrics: a disease that causes stillbirth, blindness, deafness, and permanent bone damage in newborns, yet is entirely curable with a single dose of penicillin during pregnancy. Despite this, the United States recorded its highest congenital syphilis rate in decades in 2022, with over 3,700 cases and 231 deaths. This is a failure of systems, not medicine.

How T. pallidum Crosses the Placenta
Risk of Fetal Infection by Maternal Stage
Early Congenital Syphilis: Symptoms in the First Two Years
Late Congenital Syphilis: Hutchinson's Triad and Beyond
Prenatal Screening Protocols
Newborn Evaluation: Who Needs a Workup?
Newborn Treatment: Aqueous Penicillin G ×10 Days
The Global Surge in Congenital Cases
Prevention Through Early Maternal Treatment
Key Research Papers
Featured Videos

1. How T. pallidum Crosses the Placenta

Treponema pallidum can cross the placenta and infect the fetus at any point in pregnancy, from the first trimester onward. This is different from many other congenital infections (such as rubella) that are primarily dangerous in early pregnancy; syphilis is dangerous throughout gestation.

The mechanism involves active invasion of the placental trophoblast cells by spirochetes. From there, the organisms reach fetal blood vessels and disseminate throughout the developing fetus. The placenta itself shows characteristic changes (placentitis) with enlargement, pallor, and inflammatory infiltrates that can be seen on pathologic examination.

The timing of maternal infection relative to fetal impact matters:

The fetus's immune system does not develop adequate function until around 18 to 20 weeks gestation. Before this, the fetus cannot mount an effective response to spirochetal invasion, but this may actually protect against some of the immune-mediated tissue damage seen in older children.
Most severe fetal damage and pregnancy complications occur from the second trimester onward, when the fetal immune system begins to respond to the infection with inflammatory processes that damage developing tissues.

2. Risk of Fetal Infection by Maternal Stage

The probability that an infected pregnant woman will transmit syphilis to her fetus depends heavily on the stage of her infection, which correlates with her spirochetemia (the concentration of bacteria in her blood):

Primary syphilis: Approximately 70 to 100% vertical transmission rate. The blood is teeming with spirochetes during active primary infection.
Secondary syphilis: Approximately 90 to 100% vertical transmission rate. Secondary syphilis represents peak systemic dissemination.
Early latent syphilis: Approximately 40 to 80% transmission rate. Spirochetemia continues at lower levels.
Late latent syphilis: Approximately 10 to 30% transmission rate. While bacteremia is low, transmission can still occur, and this is not negligible.
Tertiary syphilis: Low transmission rate, though cases have been reported.

The implication: maternal syphilis at any stage is dangerous to the fetus, and treatment of late latent syphilis in pregnancy is just as important as treatment of early stages.

3. Early Congenital Syphilis: Symptoms in the First Two Years

Early congenital syphilis is defined as manifestations appearing before two years of age. Symptoms may be present at birth or develop over the first weeks of life. Some infants appear entirely well at birth and become symptomatic weeks later, which makes newborn follow-up critical even when the baby looks healthy.

The most common manifestations of early congenital syphilis:

Snuffles (syphilitic rhinitis): A persistent, often blood-tinged nasal discharge in a newborn or young infant. The nasal discharge is highly infectious (teeming with spirochetes). This is one of the most characteristic signs and should trigger immediate evaluation.
Rash: A maculopapular rash similar to secondary syphilis, sometimes involving the palms and soles. Vesicular or bullous (blistering) rash on the palms and soles, called syphilitic pemphigus, is a highly characteristic severe form seen in congenital syphilis.
Hepatosplenomegaly: Enlarged liver and spleen due to spirochetal invasion and the resulting inflammatory response. Present in approximately 50 to 60% of affected newborns.
Jaundice: From hepatitis or hemolytic anemia caused by the infection.
Anemia: Often Coombs-negative hemolytic anemia from direct erythrocyte destruction or marrow suppression.
Periostitis and osteochondritis: Bone inflammation causing extreme pain on moving the limbs. Affected infants often stop moving painful limbs, a finding called pseudoparalysis of Parrot — the infant appears paralyzed from pain, not actual nerve or muscle damage. Characteristic X-ray findings include metaphyseal lucencies and periosteal reaction.
Edema: From hypoalbuminemia caused by nephrotic syndrome (syphilitic nephritis).
Failure to thrive.

Stillbirth and prematurity are the most severe outcomes. Approximately one in three untreated congenital syphilis pregnancies ends in stillbirth.

4. Late Congenital Syphilis: Hutchinson's Triad and Beyond

Late congenital syphilis refers to manifestations appearing after two years of age in children who were infected before birth but not adequately treated. Many of these findings represent the delayed sequelae of prenatal spirochetal damage to developing tissues.

Hutchinson's triad (described by Sir Jonathan Hutchinson in 1858) is the classic late congenital syphilis constellation:

Hutchinson's teeth: The upper central incisors are notched (have a central notch along the cutting edge), barrel-shaped, and wider at the gum line than at the cutting edge. The first permanent molars may show a mulberry molar pattern (clusters of small, irregular cusps). These permanent tooth changes are irreversible evidence of prenatal syphilitic damage to developing tooth germs.
Interstitial keratitis: Inflammation of the corneal stroma (the clear middle layer of the cornea), causing photophobia, pain, and progressive vision loss from corneal clouding. Occurs most commonly between ages 5 and 25. The onset is typically insidious. If untreated, it can cause permanent corneal scarring and blindness.
Eighth nerve deafness: Sensorineural hearing loss from damage to the cochlea or auditory nerve. Typically bilateral and irreversible; may be sudden in onset or progressive over years.

Other manifestations of late congenital syphilis:

Saddle-nose deformity: Collapse of the nasal bridge from destruction of the nasal cartilage and bone by early syphilitic rhinitis. The nose has a characteristic "saddle" depression at the bridge.
Saber shins: Anterior bowing of the tibia from periostitis that causes the front surface of the shinbone to thicken and become curved.
Rhagades: Radial linear scars around the mouth from healed papular eruptions of early congenital syphilis.
Clutton's joints: Painless synovitis (joint inflammation) of the knees, sometimes bilateral, from immune complex deposition.
Neurosyphilis: Cognitive difficulties, seizures, and other neurologic sequelae.

5. Prenatal Screening Protocols

Syphilis screening in pregnancy is mandatory by law in all 50 US states and is one of the most cost-effective interventions in obstetric care. The current CDC recommendations:

All pregnant women: Syphilis serologic testing at the first prenatal visit
High-risk women and high-prevalence areas: Repeat testing at 28 weeks gestation and again at delivery
Infants born to mothers whose serologic status is unknown: Should have serologic testing performed at delivery

The current epidemic has prompted calls to expand this approach. Several states have enacted legislation requiring screening at each trimester (first visit, 28 weeks, and delivery) for all pregnant women, not just high-risk populations. Analysis shows that single-visit screening misses women who acquire syphilis later in pregnancy.

A critical failure mode: women who test negative in the first trimester can acquire syphilis later in pregnancy. A woman who develops primary syphilis at 32 weeks may have a perfectly normal first-trimester screen but deliver a severely affected infant. This is why serial screening and provision of rapid testing at delivery sites matters.

6. Newborn Evaluation: Who Needs a Workup?

The CDC's algorithm for evaluating newborns for congenital syphilis considers the mother's serologic status, treatment history, and adequacy of treatment relative to delivery. In brief:

Mother with syphilis treated adequately (>4 weeks before delivery, appropriate regimen, documented serologic response): Newborn may require only neonatal serology and clinical observation, with close follow-up.
Mother treated less than 4 weeks before delivery, treated with non-penicillin regimen, or with uncertain treatment history: Full congenital syphilis workup required.
Mother untreated or inadequately treated: Full workup and empiric treatment indicated.

The full newborn workup includes:

RPR or VDRL on infant blood (not cord blood, which can give spurious results)
Complete blood count with differential and platelet count
Liver function tests
Long bone X-rays for periostitis and osteochondritis
Lumbar puncture for CSF-VDRL, cell count, and protein
Ophthalmologic examination
Neuroimaging if neurologic abnormalities are present
Auditory brainstem response testing

7. Newborn Treatment: Aqueous Penicillin G ×10 Days

For confirmed or probable congenital syphilis, the treatment is:

Aqueous crystalline penicillin G 100,000 to 150,000 units/kg/day IV, administered as 50,000 units/kg/dose every 12 hours (for the first 7 days of life) or every 8 hours (after 7 days), for a total of 10 days.

Why IV for 10 days?

Congenital syphilis is disseminated and may involve the CNS, requiring the same penetration strategy as adult neurosyphilis
The 10-day IV course ensures treponemicidal levels throughout tissues, including the CNS
Benzathine penicillin G alone is not recommended for infants with definitive or probable congenital syphilis because of inadequate CSF penetration

For a newborn born to a mother with syphilis who was adequately treated and shows no clinical or laboratory evidence of infection, a single dose of benzathine penicillin G 50,000 units/kg IM may be used as prophylaxis — but this is a clinical judgment call based on the full assessment.

Infants treated for congenital syphilis require serologic follow-up at 1, 2, 3, 6, and 12 months to confirm titer decline. An infant with an initially reactive non-treponemal test from passively transferred maternal antibodies (and not true infection) should show decline and become non-reactive by 6 months.

8. The Global Surge in Congenital Cases

Congenital syphilis has been surging in the United States for over a decade. CDC data show:

2012: 334 congenital syphilis cases reported
2017: 918 cases
2020: 2,148 cases
2022: 3,761 cases (the highest since 1992) and 231 deaths, including stillbirths

The geography is uneven: the southern and western United States carry the highest burden, with some states (California, Texas, Arizona, Oklahoma) accounting for a disproportionate share of cases. Racial disparities are stark: Black, Hispanic/Latino, and American Indian/Alaska Native infants have rates many times higher than non-Hispanic white infants, directly reflecting inequities in prenatal care access.

Analysis of congenital syphilis cases reveals a consistent pattern of missed opportunities:

Many mothers had no prenatal care at all
Some were tested but not treated (positive test result not communicated or followed up)
Some were treated too close to delivery (<30 days) to ensure adequate fetal treatment
Some were tested in the first trimester but acquired syphilis later and were not retested

9. Prevention Through Early Maternal Treatment

Every case of congenital syphilis represents a preventable outcome. The prevention pathway is straightforward:

Test. Screen all pregnant women at the first prenatal visit. Rescreen at 28 weeks and delivery in high-burden areas and for high-risk women.
Treat immediately. When a pregnant woman tests positive for syphilis, treatment should begin the same day, or within 24 to 48 hours. Do not wait for confirmatory testing before treating a pregnant woman in the third trimester. For penicillin-allergic pregnant women, desensitization and penicillin are mandatory.
Treat early enough. Treatment is considered adequate for fetal protection only if it is completed more than 30 days before delivery. Treatment within 30 days of delivery may not fully protect the fetus, and the newborn should receive a full workup and likely treatment regardless of maternal titers.
Notify and treat partners. Treating the pregnant woman while her untreated partner reinfects her during pregnancy defeats the purpose. Partner treatment is not optional.
Follow up. Confirm serologic response to treatment. If titers do not decline as expected, retreat and reassess.

These steps are not complicated. They require affordable prenatal care, reliable testing, accessible treatment, and trained public health follow-up capacity. The political and social determinants of the current epidemic — inadequate prenatal care access, substance use disrupting care, homeless population vulnerability — are the actual barriers to prevention.

Key Research Papers

Workowski KA, Bachmann LH, Chan PA, et al. Sexually transmitted infections treatment guidelines, 2021. MMWR Recomm Rep. 2021;70(4):1–187. PMID 34292926
Peeling RW, Mabey D, Kamb ML, et al. Syphilis. Nat Rev Dis Primers. 2017;3:17073. PMID 29022569
Newman L, Kamb M, Hawkes S, et al. Global estimates of syphilis in pregnancy and associated adverse outcomes: analysis of multinational antenatal surveillance data. PLoS Med. 2013;10(2):e1001396. PMID 23468598
Bowen V, Su J, Torrone E, Kidd S, Weinstock H. Increase in incidence of congenital syphilis — United States, 2012–2014. MMWR Morb Mortal Wkly Rep. 2015;64(44):1241–1245. PMID 26562453
Mobley JA, McKeown RE, Jackson KL, et al. Risk factors for congenital syphilis in infants of women with syphilis in South Carolina. Am J Public Health. 1998;88(4):597–602. PMID 9551003
Hollier LM, Cox SM. Syphilis. Semin Perinatol. 1998;22(4):323–331. PMID 9738995
Woods CR. Congenital syphilis-persisting pestilence. Pediatr Infect Dis J. 2009;28(6):536–537. PMID 19483529
Ghanem KG, Ram S, Rice PA. The modern epidemic of syphilis. N Engl J Med. 2020;382(9):845–854. PMID 32101666
Stafford IA, Workowski KA, Bachmann LH. Syphilis complicating pregnancy and congenital syphilis. N Engl J Med. 2024;390(3):242–253. PMID 38231624
Reno H, Park IU. Reproductive tract STIs: syphilis. In: UpToDate. Wolters Kluwer; 2024. — Current clinical guidance on congenital syphilis evaluation and management in routine practice.

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