Syphilis in Pregnancy
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Direct answer
Syphilis in pregnancy is infection with Treponema pallidum that can cross the placenta and cause stillbirth or congenital syphilis, so every pregnant woman is screened. Screening uses a non-treponemal test such as VDRL or RPR, confirmed by a treponemal test. Benzathine penicillin G is the only adequate treatment in pregnancy, and the number of doses depends on the stage of disease, with partner treatment and repeat titres required.
What you must remember
- Screening: VDRL or RPR is sent at booking; a reactive result is confirmed with a treponemal assay such as TPHA or an enzyme immunoassay, because non-treponemal tests can be falsely positive.
- Treatment: Benzathine penicillin G 2.4 million units intramuscularly as one dose for early syphilis, and as three weekly doses for late latent or unknown duration.
- Penicillin allergy: Penicillin is the only recommended treatment in pregnancy, so an allergic woman is desensitised rather than given an alternative drug.
- Early congenital features: Hepatosplenomegaly, snuffles, a desquamating rash of palms and soles, periostitis, anaemia and hydrops.
- Late congenital features: Hutchinson's triad of interstitial keratitis, Hutchinson teeth and eighth nerve deafness, with mulberry molars and saddle nose.
- Adequate treatment: Penicillin completed at least 30 days before delivery counts as adequate; otherwise the newborn is evaluated and treated with aqueous penicillin G.
Staging, screening and treatment, step by step
A positive serology must be staged before treatment, because the stage sets the penicillin schedule. The steps below follow the order used at most antenatal clinics.
- Screen at booking: Test at the first antenatal visit with a non-treponemal test, and repeat in the third trimester and at delivery where risk is high, as per current national guidance.
- Confirm the result: A reactive non-treponemal test is confirmed with a treponemal assay. Treponemal tests stay reactive for life, so they cannot be used to judge cure.
- Stage the infection: Take a history of chancre, rash, symptoms and previous treatment; early syphilis is under one year in duration, and late latent syphilis is longer or unknown.
- Treat by stage: Give one dose of benzathine penicillin G for primary, secondary or early latent disease, and three weekly doses for late latent or unknown duration.
- Monitor response: Repeat the non-treponemal titre; a fourfold fall is the expected response, and no fall prompts reassessment.
- Manage the partner and newborn: Treat sexual partners and plan neonatal evaluation when treatment was incomplete or finished less than 30 days before delivery.
Where the examiner tries to catch you
Most syphilis questions turn on timing, the choice of drug and the newborn examination.
- Trap: Choosing azithromycin or doxycycline for a pregnant woman with penicillin allergy Correct: Desensitise her to penicillin, because the alternatives are not considered adequate to treat the fetus.
- Trap: Reading a positive VDRL as proof of active disease Correct: Non-treponemal tests can be falsely positive in autoimmune disease and some other infections, so a treponemal test confirms the diagnosis.
- Trap: Assuming congenital syphilis is always visible at birth Correct: Many infected newborns look normal, so features emerge in the first weeks and the infant must be followed.
Frequently asked questions
Which test is used to screen for syphilis in pregnancy?
Screening uses a non-treponemal test such as VDRL or RPR at the first antenatal visit. A reactive result is confirmed with a treponemal test before treatment, and the non-treponemal titre is then used to monitor the response to therapy.
What is the drug of choice for syphilis in pregnancy?
Benzathine penicillin G is the drug of choice for syphilis in pregnancy at every stage. The number of doses depends on the stage, with one intramuscular dose for early syphilis and three weekly doses for late latent syphilis.
What are the features of early congenital syphilis?
Early congenital syphilis, seen before about two years of age, causes hepatosplenomegaly, rhinitis called snuffles, a desquamating rash on palms and soles, and periostitis. Anaemia, jaundice, lymphadenopathy and hydrops may also be present at birth.
Why is a newborn evaluated when maternal penicillin was given close to delivery?
CDC regards a mother as adequately treated when penicillin is completed at least 30 days before delivery. If treatment was incomplete or finished less than 30 days before delivery, the newborn is evaluated and treated with aqueous penicillin G.