Infections That Cause Preterm Labor: What Expectant Mothers Should Know

Understanding the Link Between Infection and Preterm Labor

Preterm labor, which is labor beginning before 37 completed weeks of pregnancy, can be caused by a variety of factors. One of the most significant and often preventable is infection. In fact, research suggests that about 40% of spontaneous preterm labors are associated with infection or inflammation (CDC), (ObGyn Key).^1,2

This makes it especially important for expectant mothers to understand how infections that cause preterm labor develop, how they are detected, and what can be done to lower the risk.

Why Do Infections Cause Preterm Labor?

When infections enter the genital tract or uterus, the body responds with inflammation. This inflammation releases chemicals like cytokines and prostaglandins, which can weaken the membranes around the baby, potentially causing them to rupture. It may also trigger contractions, leading to preterm labor.

The Role of Intrauterine Infection and Inflammation

Some infections, called intrauterine infections, may not cause symptoms but still create complications. One possible outcome is chorioamnionitis, a serious condition where the placenta and surrounding tissues become inflamed. Infections can also reach or damage the amniotic fluid, increasing the risk of early labor and preterm delivery.

Common Infections That Cause Preterm Labor

Several common bacterial and sexually transmitted infections have been linked to preterm birth.

Bacterial Vaginosis (BV)

Bacterial vaginosis (BV) occurs when the natural balance of bacteria in the vagina is disrupted. This condition may cause abnormal vaginal discharge or odor, but sometimes it has no symptoms at all. Studies show BV is a leading contributor to infection-related preterm birth, especially when it appears during the second trimester.

Chlamydia Trachomatis

Chlamydia trachomatis is a common sexually transmitted infection (STI) that often goes unnoticed. When present during pregnancy, it can lead to inflammation in the genital tract, increasing the risk of preterm labor and potential neonatal infections. Fortunately, it’s treatable with antibiotics when caught early.

Neisseria Gonorrhoeae (Gonorrhea)

Gonorrhea, caused by the Neisseria gonorrhoeae bacteria, is another STI that can cause complications in pregnancy. Like Chlamydia, it is often asymptomatic. It can infect the amniotic fluid, increase the risk of chorioamnionitis, and contribute to neonatal sepsis, a serious blood infection in newborns.A study published in JAMA Network Open (2016–2019) found that maternal STIs, including Chlamydia, Gonorrhea, and Syphilis, significantly increase the risk of preterm birth.³

Asymptomatic Bacteriuria

Asymptomatic bacteriuria refers to the presence of bacteria in the urine without noticeable symptoms. If left untreated, it can develop into a kidney infection and potentially lead to preterm labor. That’s why routine pregnancy care often includes screening and treatment for urinary tract infections, even when no symptoms are present.

How Infections Are Detected During Pregnancy

Routine prenatal care includes screenings for urinary tract infections and STIs, helping providers catch potential risks early. Some infections, however, don’t show symptoms, making early testing crucial. Others may only be discovered after premature rupture of membranes or during early labor.

When to Talk to Your Provider

You should contact your provider if:

• You have a history of preterm birth or early labor
• You experience abnormal vaginal discharge, fever, or pelvic pain
• You’ve tested positive for any infection or have concerns about symptoms

The PreTRM® Test is a blood test that measures proteins (biomarkers) associated with preterm birth risk—not infections. While it doesn’t detect infections, it can help assess your overall risk of preterm delivery before symptoms appear. Ask your provider if the PreTRM® Test is right for your pregnancy.

The Bigger Picture: Multiple Pathogens and Preterm Birth Risk

Researchers have found several pathogens that may disrupt the genital tract environment and increase inflammation in the uterus, amniotic fluid, or membranes. These include:

• Ureaplasma urealyticum
• Mycoplasma hominis
• Group B Streptococcus
• Gardnerella vaginalis
• Chlamydia trachomatis
• Neisseria gonorrhoeae

According to the CDC and ObGyn Key, infection and inflammation are involved in nearly 40% of all spontaneous preterm labors, especially those before 32 weeks.^1,2

Research from MDPI connects infection-related preterm birth to serious neonatal outcomes, including long-term health challenges and increased risk of mortality.⁴

Protecting Your Pregnancy From Infection-Related Preterm Labor

What You Can Do

Here are some simple steps to help lower your risk:

• Attend all scheduled prenatal appointments
• Ask about early screening for STIs and urinary tract infections
• Avoid douching, which disrupts healthy vaginal microflora
• Practice safe sex and limit exposure to infections
• Speak up if you’ve had a previous preterm birth or are concerned about infection risks

Why Early Risk Assessment Matters

Not all cases of preterm labor can be prevented, but knowing your risk ahead of time allows for better planning. Tools like the PreTRM® Test use biomarker data to identify your personalized risk for delivering early, even if you have no risk factors. While it doesn’t detect infection-related risks, it can support earlier, more informed care planning with your provider.

Key Takeaways

Understanding the impact of infections that cause preterm labor can empower you to make informed, confident decisions throughout your pregnancy journey. Prevention starts with awareness, open communication, and early action.

References

1. CDC: “Grand Rounds: Public Health Strategies to Prevent Preterm Birth”
2. ObGyn Key: “Chapter 22 – Infections and Preterm Labour”
3. JAMA Network: “Association of Maternal STIs With Risk of Preterm Birth”
4. MDPI: “Maternal Infection and Preterm Birth”