(699) STI coinfection does not increase congenital syphilis in gravidas effectively treated for syphilis in pregnancy

Evaluate the impact of sexually transmitted (STI) co-infection pregnancy on maternal syphilis and congenital syphilis outcomes.

Study Design:
In this retrospective cohort study, we identified pregnant patients with syphilis delivering at a large, public hospital. We excluded those with syphilis treatment prior to pregnancy, unless early infection was diagnosed during the current pregnancy. We reviewed medical records for coinfection with other STIs during the current pregnancy, including chlamydia, gonorrhea, HIV, and hepatitis B and C. We compared demographics, comorbidities, reported substance use, maternal syphilis characteristics and neonatal outcomes to determine the impact of STI coinfection on syphilis-associated neonatal outcomes.

Results:

From January 1, 2010 through June 30, 2025, 581 gravidas with syphilis were included, with 166(28.6%)  diagnosed with an STI co-infection. Chlamydia was most frequent 117(70%), followed by gonorrhea in 39(23%), hepatitis C in 24(15%), HIV in 19(11%), and hepatitis B in 6(4%). Patients with co-infections were younger (24.4 v. 26.0, p=0.005) and more likely to have comorbid substance use (36% v. 26%, p=0.01). Patients with STI coinfection were diagnosed with syphilis later (21.5 vs 17.0 weeks, p=0.04), had fewer prenatal care visits, and were more likely to have early syphilis stage (66[40%] vs 110[27%], p=0.002). Frequency of benzathine penicillin G (BPG) administration before delivery was high in both groups.  Syphilis-exposed neonates born to individuals with co-infection had lower birthweight after adjustment for the effect of maternal age and substance use. Infants born to individuals with STI co-infections were not at increased risk for congenital syphilis after adjusting for maternal age, substance use and early syphilis stage.

Conclusion:

STI co-infection with maternal syphilis occurred in over 28% and was associated with maternal substance use and reduced prenatal care. While neonates had significantly lower birth weight, maternal STI coinfection was not independently associated with increased congenital syphilis.