Syphilis screening is a routine and mandatory part of prenatal care across the United States, established to safeguard the health of the pregnant person and the developing fetus. This screening aims to detect a bacterial infection caused by Treponema pallidum, which can have devastating consequences if left untreated during pregnancy. Early identification and subsequent treatment are key public health measures that effectively prevent the transmission of this disease from parent to child.
What Syphilis Is and How It Spreads
Syphilis is an infection caused by the spirochete bacterium Treponema pallidum, which progresses through several distinct stages. It is primarily transmitted through direct sexual contact with an active sore, known as a chancre, which appears during the primary stage. This initial sore is often painless and may go unnoticed.
If untreated, the infection progresses to the secondary stage, characterized by a non-itchy, diffuse rash that frequently involves the palms and soles. Following the secondary stage, the infection enters a latent period, producing no visible signs or symptoms while the bacteria remain in the body. The infection can also be transmitted vertically from the pregnant person to the fetus through the placenta at any stage of the disease.
The Risk of Congenital Syphilis
The primary reason for universal prenatal screening is the severe threat posed by congenital syphilis, which occurs when the Treponema pallidum bacteria passes from the pregnant person to the fetus. The risk of transmission is highest during the early stages of maternal infection, but it can happen at any time. Untreated syphilis in pregnancy carries a high risk of adverse outcomes, including miscarriage, preterm birth, and stillbirth.
For infants who survive, the infection can cause serious, lifelong medical issues. Complications include bone deformities, severe anemia, enlarged liver and spleen, and neurological problems such as blindness or deafness. The rising incidence of this preventable disease underscores the screening’s importance, with cases of congenital syphilis in the U.S. having increased by nearly 700% since 2015, with close to 4,000 cases reported in 2024.
Screening Protocols During Pregnancy
Syphilis testing is recommended for all pregnant individuals at the first prenatal visit, and this initial screening is mandated by law in most states. The screening is performed via a simple blood draw and involves a two-step testing algorithm to ensure accuracy. The first step uses a nontreponemal test, such as the Rapid Plasma Reagin (RPR) or Venereal Disease Research Laboratory (VDRL) test, which detects antibodies produced in response to tissue damage.
Any reactive nontreponemal test result is followed by a treponemal test, which confirms the presence of antibodies specific to the Treponema pallidum bacterium. For individuals at high risk for acquiring the infection, or those living in areas with high rates of syphilis, repeat screening is performed. Retesting is typically scheduled for the third trimester, around 28 weeks of gestation, and again at the time of delivery.
Treatment and Follow-Up Management
If screening tests return a positive result, immediate treatment is initiated to cure the infection and prevent transmission to the fetus. Benzathine Penicillin G is the medication of choice and the only treatment proven effective for both the pregnant person and the fetus. For early-stage syphilis, this involves a single intramuscular dose, while late latent syphilis requires three weekly doses.
Pregnant individuals with a documented penicillin allergy must undergo a desensitization process to safely receive the medication. Alternatives like doxycycline and tetracycline are avoided due to the potential for fetal harm. Following treatment, quantitative nontreponemal tests (titers) are regularly monitored to ensure success; a fourfold decrease in the titer is the expected sign of a positive response.
The infant’s treatment protocol is determined by the mother’s serologic status at delivery and the adequacy of her treatment. If maternal treatment was incomplete or given too close to delivery, the newborn may still require a full evaluation and a 10-day course of intravenous or intramuscular penicillin. Careful serologic follow-up of the infant is necessary until the nontreponemal antibodies disappear, confirming the absence of congenital infection.