Perinatal infections IV: syphilis in pregnancy and other sexually transmitted infections

A 24-year-old books at 14 weeks. Her RPR is reactive at 1:32 with a positive TP-PA. She is 18 weeks pregnant by the time you see her, allergic to penicillin, and anxious. Three decisions sit on you: stage the disease, treat it adequately, and protect the fetus from congenital syphilis — all while the clock on transplacental transmission is ticking. Syphilis in pregnancy is the answer that tests whether you know the one drug, the number of doses, the reaction to expect, and the titre that proves you succeeded.^[1][11]

Overview and definition

Syphilis is caused by the spirochaete Treponema pallidum, and in pregnancy it does two things at once: it infects the woman through the recognised stages, and it crosses the placenta to infect the fetus. The antenatal job is to treat the woman early enough and adequately enough to prevent congenital syphilis, while the disease is still responsive to a single agent — penicillin.^[1][12]

The two pieces of definition examiner wants:^[1][4]

• Maternal staging drives the dose. Primary (chancre), secondary (rash, palms and soles, condylomata lata), early latent (asymptomatic, under one year's duration), late latent (over one year or unknown duration), tertiary (gummatous, cardiovascular), and neurosyphilis (ocular, otic, meningovascular). The stage decides whether you give one dose or three.
• Serological confirmation is two tests, doing two jobs. Non-treponemal tests (RPR, VDRL) screen and monitor response with a quantitative titre. Treponemal tests (TP-PA, FTA-ABS, chemiluminescent immunoassay) confirm, and stay positive for life. Treponemal tests do not monitor response.^[1]

^{[1] [2]}

References12ShowHide

1. [1]Workowski KA, Bachmann LH, Chan PA, et al. Sexually Transmitted Infections Treatment Guidelines, 2021 MMWR Recomm Rep, 2021.PMID 34292926
2. [2]Klein VR, Cox SM, Mitchell MD, et al. The Jarisch-Herxheimer reaction complicating syphilotherapy in pregnancy Obstet Gynecol, 1990.PMID 2304710
3. [3]Walker GJ Antibiotics for syphilis diagnosed during pregnancy Cochrane Database Syst Rev, 2001.PMID 11686978
4. [4]Walker GJ, Walker DG Congenital syphilis: a continuing but neglected problem Semin Fetal Neonatal Med, 2007.PMID 17336171
5. [5]Kaminiów K, Kotlarz A, Kiołbasa M, et al. Single versus three doses of benzathine penicillin G for early syphilis in pregnancy: no added benefit in serological response or neonatal outcomes Sex Transm Infect, 2026.PMID 41314798
6. [6]Tong H, Heuer A, Walker N The impact of antibiotic treatment for syphilis, chlamydia, and gonorrhoea during pregnancy on birth outcomes: a systematic review and meta-analysis J Glob Health, 2023.PMID 37325885
7. [7]St Cyr S, Barbee L, Workowski KA, et al. Update to CDC's Treatment Guidelines for Gonococcal Infection, 2020 MMWR Morb Mortal Wkly Rep, 2020.PMID 33332296
8. [8]Davidson KW, Barry MJ, Mangione CM, et al. Screening for Chlamydia and Gonorrhea: US Preventive Services Task Force Recommendation Statement JAMA, 2021.PMID 34519796
9. [9]Kissinger PJ, Gaydos CA, Seña AC, et al. Diagnosis and Management of Trichomonas vaginalis: Summary of Evidence Reviewed for the 2021 Centers for Disease Control and Prevention Sexually Transmitted Infections Treatment Guidelines Clin Infect Dis, 2022.PMID 35416973
10. [10]Diav-Citrin O, Shechtman S, Gotteiner T, et al. Pregnancy outcome after gestational exposure to metronidazole: a prospective controlled cohort study Teratology, 2001.PMID 11320529
11. [11]Desjardins AA, Amaral E, Miranda J, et al. Syphilis in pregnancy: a practical guide for prenatal care providers Int J Gynaecol Obstet, 2025.PMID 40977496
12. [12]Berman SM Maternal syphilis: pathophysiology and treatment Bull World Health Organ, 2004.PMID 15356936