Syphilis Test in Pregnancy: Why It Matters and What to Expect

Syphilis testing in pregnancy is not optional — it's a standard of care in all 50 US states, and the consequences of missed diagnosis are severe and entirely preventable. All pregnant women should be tested for syphilis at the first prenatal visit; women in high-prevalence areas or at increased risk should be retested at 28 weeks and at delivery; treatment with benzathine penicillin G before 36 weeks prevents congenital syphilis with near-complete efficacy; and the ongoing US congenital syphilis crisis — over 3,700 cases and 282 stillbirths in 2022 — is a healthcare access failure, not a medical failure.

Why Syphilis Testing in Pregnancy Is Mandatory

Untreated maternal syphilis during pregnancy causes congenital syphilis — infection of the fetus via placental transmission from approximately 9 to 10 weeks of gestation onward. The outcomes of untreated congenital syphilis include: miscarriage and stillbirth; premature birth; neonatal death; and severe neonatal syphilis affecting bone (periostitis, osteochondritis causing "pseudoparalysis"), liver, skin (pemphigus syphiliticus), brain (meningoencephalitis), and eyes (interstitial keratitis). Transmission rates vary by maternal stage: primary or secondary syphilis carries 70 to 100% transmission risk; early latent approximately 40%; late latent less than 10%. In the US, syphilis testing at the first prenatal visit is legally required or strongly mandated in all 50 states. Despite this, the US congenital syphilis rate has risen dramatically since 2015, primarily affecting women who either didn't receive prenatal care or received it late.

The Syphilis Test: What It Is and How to Interpret It

Syphilis testing uses a two-step process: a non-treponemal test (RPR — Rapid Plasma Reagin, or VDRL) followed by a confirmatory treponemal test (TPPA, FTA-ABS, or EIA) if the screening test is reactive. RPR/VDRL: detects non-specific antibodies that appear in syphilis but can also be reactive in other conditions (false positives in pregnancy due to non-specific immune activation, autoimmune conditions, recent infections). A reactive RPR in pregnancy always requires confirmatory treponemal testing before treatment decisions. Treponemal tests (TPPA, FTA-ABS): detect antibodies specific to Treponema pallidum

When to Retest During Pregnancy

First prenatal visit (ideally before 12 weeks): all pregnant women. 28 weeks: women in high-prevalence areas, women with risk factors (new partners, sex work, drug use, partner with multiple partners), or in jurisdictions requiring it. At delivery: all women in high-prevalence areas; women without documented third-trimester testing; all women when state policy requires it. A negative first-trimester syphilis test does not rule out infection acquired later in pregnancy.

Treatment in Pregnancy

Benzathine penicillin G is the only recommended treatment for syphilis in pregnancy. It is safe throughout pregnancy and crosses the placenta to treat the fetus. No alternative antibiotics (doxycycline, azithromycin, ceftriaxone) have demonstrated adequate fetal protection for congenital syphilis prevention. The Jarisch-Herxheimer reaction may occur 2 to 8 hours after the first penicillin dose — a temporary reaction involving fever, chills, malaise, and sometimes fetal heart rate changes from rapid spirochete death. It is not an allergic reaction. Management: acetaminophen and monitoring; hospitalization if advanced pregnancy or concerning fetal status. Penicillin-allergic pregnant women require skin testing and desensitization before treatment — not penicillin avoidance.

Follow-Up After Treatment

Test of cure: repeat RPR titer at 28 to 32 weeks and at delivery to monitor treatment response. A 4-fold decline in RPR titer confirms adequate treatment. If titer doesn't decline adequately: consider re-treatment. Neonatal evaluation: neonates born to mothers with reactive syphilis serology require evaluation and may need treatment regardless of maternal treatment status.

For syphilis RPR and treponemal testing with results in 1 to 2 days, Health Test Express offers panels without a GP referral.

Frequently Asked Questions

Is syphilis testing routine in pregnancy?

Yes. Syphilis testing at the first prenatal visit is required or strongly mandated by law in all 50 US states. It's as routine as blood type testing and rubella immunity assessment.

Can a false positive syphilis result occur in pregnancy?

Yes. Non-treponemal tests (RPR, VDRL) can be reactive in pregnancy due to non-specific immune changes. This is why a reactive RPR always requires confirmatory treponemal testing before a diagnosis of syphilis is made or treatment initiated. A reactive RPR with a negative treponemal test in a pregnant woman is likely a biological false positive.

What happens if syphilis is detected in the third trimester?

Immediate treatment with benzathine penicillin G (with stage-appropriate dosing). Treatment before 30 weeks prevents most adverse outcomes; treatment after 30 weeks still significantly reduces risk. No untreated syphilis in pregnancy is safe — treat as soon as diagnosed, regardless of trimester.

Related: Syphilis symptoms in women · How does syphilis spread? · STD testing during pregnancy · Get tested today

This article is for informational purposes only and does not constitute medical advice.