Syphilis in Pregnancy

What a positive screening test does and does not tell you

This is the single most important thing to understand, and the NHS IDPS handbook states it directly: "a positive antenatal syphilis screening result cannot differentiate between a current syphilis infection and past syphilis infection which was successfully treated, therefore a comprehensive assessment must be carried out by sexual health services for all pregnant women with confirmed positive results, to make a clear maternal diagnosis and treatment plan."

If you were treated for syphilis years ago, your test can still be positive. If you have never had syphilis, a screening test can be reactive for other reasons and needs confirmatory testing. A positive result is the start of an assessment, not a diagnosis.

For scale, the handbook records around 1,000 cases of syphilis in pregnancy each year in England, with "just under half of those" requiring treatment in pregnancy, a mix of new diagnoses and previously diagnosed infections needing treatment or re-treatment. Screen positive rates rose from 1.39 per 1,000 tested in 2017 to 2018 to 1.59 per 1,000 tested in 2020 to 2021.

The timeframes

Syphilis follows the same NHS pathway timings as HIV and hepatitis B. Laboratory results should be available to maternity services within 8 working days. A confirmed screen positive result should be followed by an appointment offered within 5 working days of the maternity service being notified. An inconclusive result triggers a repeat sample taken at least 2 weeks after the first, and the handbook advises against referral to sexual health services unless that repeat confirms infection, specifically to avoid unnecessary distress.

Since May 2023 the IDPS programme has run a dedicated syphilis management pathway aimed at improving the timeliness of entry into specialist care, with roles, responsibilities and timeframes defined, and consistent with the British Association for Sexual Health and HIV syphilis guideline.

Treatment, and the 30-day rule

The handbook says syphilis "should be treated with penicillin which is extremely effective (success rate of 98%) in preventing transmission to the baby". ACOG's practice advisory says the same in different words: "benzathine penicillin G is the only known effective treatment for syphilis in pregnancy and the prevention of congenital syphilis", with desensitisation followed by penicillin recommended where there is a known severe penicillin allergy. This page names the antibiotic and gives no dose.

The timing point is the one to hold onto. The handbook states that "the highest risk of transmission during pregnancy is in the third trimester", and that "congenital syphilis is more likely to occur when a woman has primary or secondary syphilis and is treated less than 30 days before delivery". Treatment completed well before birth is what protects the baby, which is exactly why the pathway is built around speed rather than convenience.

What untreated infection can do

These figures are frightening and they describe untreated infection, which is the whole point of screening. The handbook says congenital syphilis can cause miscarriage or late fetal loss, stillbirth and neonatal death, and that "it is estimated that up to 40% of babies with congenital syphilis may be stillborn or die as a newborn". Among live births, it can cause low birth weight, jaundice, severe anaemia and neurological complications.

WHO's global figure is that syphilis in pregnancy, "when not treated, treated late or treated with the incorrect antibiotic, results in 50-80% of cases with adverse birth outcomes". WHO estimates 8 million adults aged 15 to 49 acquired syphilis in 2022.

Read the denominators. The 40% figure describes babies who already have congenital syphilis, not babies born to women with a positive screening test. The UK pathway exists to stop the first group forming.

Why it is missed outside pregnancy

The handbook describes the natural history and it explains why screening is universal rather than symptom-triggered. The primary stage is a chancre that "is usually (but not always) firm, round, and painless", may occur where it is hard to notice, and heals on its own in 3 to 6 weeks whether or not it is treated. Secondary stage symptoms, present in around 25% of cases, include rashes that "may be so faint they are hard to notice" and go away with or without treatment. Latent syphilis has no visible signs at all and can last for years.

So a negative history means very little. That is not a reflection on anyone; it is a property of the infection.

Partners, re-infection and your baby

The handbook notes that women treated in pregnancy may be re-infected, so partner testing and treatment matter as part of your own care rather than as an afterthought.

All babies born to mothers treated for syphilis in the current pregnancy require neonatal review at birth including full physical examination and syphilis serology. The handbook warns that a baby born with congenital syphilis "may not have any immediate signs or symptoms", which is precisely why the follow-up is done regardless of appearance, and says infants diagnosed with congenital syphilis should be treated with penicillin without delay.

Screening policy elsewhere

Policies differ. ACOG updated its position in 2024 so that obstetric professionals "should screen all pregnant individuals serologically for syphilis at the first prenatal care visit, followed by universal rescreening during the third trimester and at birth, rather than use a risk-based approach". It cites a 755% increase in US congenital syphilis cases between 2012 and 2021 and 3,755 cases in 2022 alone, with 88% judged preventable by timely screening and treatment. The English programme screens at booking, with repeat testing recommended if circumstances change. Those are different national policies responding to different epidemiology, and neither is a correction of the other.