STI Testing During Pregnancy Lowers Risk Of Preterm Birth, Trial Finds

Screening and treating pregnant women for common STIs might lower their risk of a preterm birth, a new clinical trial reports.

Screening for three common sexually transmitted infections twice during pregnancy reduced the risk of preterm birth by 23%, researchers reported recently in the journal Clinical Infectious Diseases.

“Complications from preterm birth are among the leading causes of death among children under 5 years of age globally,” said lead researcher Andrew Medina-Marino, an adjunct associate professor of psychiatry at the University of Pennsylvania.

“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,” Medina-Marino said in a news release.

The trial focused on three common and treatable STIs — chlamydia, gonorrhea and trichomoniasis. These have been linked to both preterm birth and low birth weight.

For the study, researchers recruited more than 2,200 pregnant women at four government health clinics in South Africa and randomly assigned them to one of three groups:

• One group received STI screening at their first prenatal visit, with follow-up treatment and testing for those who tested positive.

• Another group received screening at their first visit and again between 30 and 34 weeks of pregnancy.

• A third group received standard care, in which they received STI screening only if they showed any symptoms of infection.

About 27% of women screened at the start of the study tested positive for at least one of the three STIs, the study found. In 4 out of 5 of those cases (80%), the infected women showed no signs or symptoms.

“Because most of the infections we found caused no symptoms, waiting for symptoms alone means we may miss an opportunity to intervene,” Medina-Marino said.

Overall, nearly 19% of women who went untested had a preterm birth, compared with under 15% of those tested twice during pregnancy.

Screening only once was not associated with lower odds of preterm birth, researchers reported.

About 9% of women screened again in the third trimester tested positive for an STI during that visit, researchers said.

However, researchers noted that women screened twice did not have a significant reduction in both preterm births and low birthweight combined. Screening also did not reduce the odds of low birthweight only.

“The results give us an important signal, but they don’t settle the question of how often pregnant patients should be screened,” Medina-Marino said. “The next step is understanding when screening can have the greatest impact and which patients are most likely to benefit.”

More information

The U.S. Centers for Disease Control and Prevention has more on STIs and pregnancy.

SOURCE: University of Pennsylvania, news release, Oct. 29, 2026