A randomized clinical trial shows two rounds of testing for chlamydia, gonorrhea, and trichomoniasis identified mostly asymptomatic infections and reduced preterm deliveries.
Screening and treating pregnant patients for three common sexually transmitted infections (STIs) twice during pregnancy is associated with a 23% lower risk of preterm birth compared with standard care, according to a randomized clinical trial published in Clinical Infectious Diseases.
The study, led by researchers at the University of Pennsylvania and the University of Southern California, evaluated screening for chlamydia, gonorrhea, and trichomoniasis. In the trial, 14.5% of participants who received diagnostic screening and targeted treatment twice during pregnancy experienced a preterm birth, compared with 18.8% of individuals receiving standard care based on syndromic management. Screening participants only once during pregnancy showed no benefit, resulting in a preterm birth rate of 18.9%.
“Complications from preterm birth are among the leading causes of death among children under five years of age globally. This study suggests that testing for STIs during pregnancy could help us find and treat infections that might otherwise go unnoticed, and that screening more than once may be important for reducing the risk of preterm birth,” says Andrew Medina-Marino, PhD, adjunct associate professor of psychiatry at the University of Pennsylvania Perelman School of Medicine and co-lead author of the study, in a release. “Because most of the infections we found caused no symptoms, waiting for symptoms alone means we may miss an opportunity to intervene.”
Asymptomatic Infections Dominate Trial Cohort
The randomized clinical trial enrolled 2,247 pregnant participants across four government health clinics in South Africa, entering care at a median gestational age of 13 weeks. Participants were randomized into one of three arms:
- Screening and treatment at the initial antenatal visit with a test-of-cure three weeks later for confirmed infections
- Screening and treatment at the initial visit and again between 30 and 34 weeks of gestation
- Standard care, where diagnostic evaluation and treatment were triggered only by clinical symptoms
At baseline, approximately 27% of participants tested positive for at least one of the three STIs. Notably, approximately 80% of those detected infections were entirely asymptomatic, underscoring the clinical limitations of symptom-triggered testing protocols.
Among participants rescreened in the third trimester, 9.2% tested positive for an STI. Investigators reported that these third-trimester cases included persistent or recurrent infections, as well as incident infections in patients who had previously tested negative earlier in pregnancy.
Diagnostic Implications and Next Steps
While the twice-during-pregnancy screening protocol demonstrated a significant reduction in preterm birth alone, it did not significantly reduce the trial’s primary composite outcome of preterm birth or low birthweight, nor did it lower low birthweight when evaluated independently. Consequently, the study authors emphasize that the findings warrant further clinical investigation.
“The results give us an important signal, but they don’t settle the question of how often pregnant patients should be screened,” says Medina-Marino in a release. “The next step is understanding when screening can have the greatest impact and which patients are most likely to benefit.”
Study authors highlighted limitations, including the trial’s setting in a single South African region with high STI prevalence, which may affect generalizability to broader patient populations. Additionally, the trial was not powered to identify specific patient subgroups that derived the most benefit.
Despite these limitations, the investigators noted that the data contribute key evidence regarding the timing, frequency, and clinical utility of prenatal diagnostic screening protocols, including potential applications in higher-income nations such as the US.
The trial received funding from the National Institute of Allergy and Infectious Diseases through grant R01AI149339.
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