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Chorioamnionitis and Premature Births: Is There a Controversial Outcome?

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Lena Voss in Health & Wellness June 2025 • 4 min read.

"Exploring the link between chorioamnionitis and outcomes for preterm infants, examining the controversial research and potential preventative strategies."


The journey of pregnancy is often celebrated as a miracle, but it can also be fraught with complications. One such complication is chorioamnionitis, an infection or inflammation of the fetal membranes (the amnion and chorion). This condition can occur in both mixed fetal-maternal (choriodecidual space) and fetal origins (chorioamniotic membranes, amniotic fluid, umbilical cord).

Chorioamnionitis is identified using various methods, including histological, microbiological, biochemical, and clinical criteria. Histopathological examination of the placenta remains the gold standard for assessing antenatal inflammatory processes, which can significantly influence fetal development. Understanding this condition is critical because it's a leading cause of preterm delivery, with its incidence increasing as gestational age decreases. Consequently, chorioamnionitis contributes to the morbidity and mortality of prematurely born infants.

Over the past decades, researchers have worked hard to understand the effects of chorioamnionitis on neonatal and long-term outcomes, but the findings have been inconsistent. These discrepancies are often due to different inclusion and exclusion criteria, variations in disease definitions and research methods, and whether confounding factors like gestational age were considered. It is important to clarify the link between antenatal infection/inflammation and both short- and long-term outcomes for these babies.

How Does Chorioamnionitis Develop and What Role Does It Play in Preterm Birth?

Protective womb symbolizing medical breakthroughs in neonatal care.

Intrauterine infections can occur in several ways, including through the decidua materna (between maternal tissues and fetal membranes), the fetal membranes themselves (chorion and amnion), the placenta, amniotic fluid, umbilical cord, and even the fetus. Chorioamnionitis, strictly defined as an infection/inflammation of the chorion and amnion, is often used to describe any intrauterine infection/inflammation affecting the fetal membranes and other fetal annexes.

Infection is a significant cause of preterm birth. The first study to provide substantial microbiological evidence of the link between intrauterine infection before membrane rupture and preterm labor was in 1977, when Bobitt et al. isolated bacteria from the amniotic fluid of 7 out of 10 women in preterm labor with intact membranes. Subsequent studies suggest that intrauterine infection may account for 25-40% of preterm births. However, this may be underestimated because infection can be difficult to diagnose due to the limitations of traditional culture methods and challenges in sampling amniotic fluid.

  • Ascending Infection: Microorganisms travel from the vagina and cervix.
  • Hematogenous Transmission: Bacteria spread through the placenta.
  • Retrograde Transmission: Infection moves from the peritoneal cavity via the fallopian tubes.
  • Iatrogenic Introduction: Accidental introduction during invasive procedures like amniocentesis.
The ascending route is the most common. Microorganisms move up from the lower genital tract, first colonizing the choriodecidual space and then crossing the amniotic membranes to reach the amniotic cavity and fetus. Researchers are still unsure about when bacteria most frequently ascend into the amniotic cavity during pregnancy, but there is significant evidence that intrauterine infection is often a chronic rather than acute condition. Infections can begin early in pregnancy and remain undetected for months.

Striking a Balance: Future Directions in Research and Care

Despite conflicting research findings, the possibility that intrauterine infection/inflammation increases the risk of adverse outcomes for preterm infants cannot be ruled out. This warrants careful evaluation and further research to understand the mechanisms linking intrauterine infection/inflammation to premature birth. By identifying strategies to guide clinical decisions in diagnostics and therapeutics—both for maternal care (e.g., identifying at-risk women and determining the best timing for delivery) and neonatal care—we can improve outcomes for this vulnerable population.

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Everything You Need To Know

1

What exactly is chorioamnionitis?

Chorioamnionitis refers to an infection or inflammation of the fetal membranes, specifically the amnion and chorion. It can originate from both maternal and fetal sources, affecting areas like the choriodecidual space, amniotic fluid, and umbilical cord. Histopathological examination of the placenta is the standard method for identifying antenatal inflammatory processes. Recognizing this condition is vital as it is a major cause of preterm delivery and can significantly affect the health of premature infants.

2

How does intrauterine infection lead to premature birth?

Intrauterine infections, including chorioamnionitis, can lead to preterm birth through various pathways. Microorganisms can ascend from the vagina and cervix, spread through the placenta via hematogenous transmission, move from the peritoneal cavity via retrograde transmission, or be introduced during invasive procedures. Ascending infection, where microorganisms travel from the lower genital tract, is the most common. Research indicates that these infections are often chronic and can begin early in pregnancy, remaining undetected for months.

3

How is chorioamnionitis diagnosed?

Chorioamnionitis is typically diagnosed using histological, microbiological, biochemical, and clinical criteria. Histopathological examination of the placenta serves as the gold standard for assessing antenatal inflammatory processes. While microbiological methods can identify specific pathogens, they are limited by traditional culture methods and challenges in sampling amniotic fluid, making diagnosis complex.

4

Why are the research findings on chorioamnionitis so inconsistent?

Research findings on the effects of chorioamnionitis on neonatal and long-term outcomes have been inconsistent due to variations in study designs, diagnostic criteria, and the consideration of confounding factors like gestational age. Clarifying the link between antenatal infection/inflammation and both short- and long-term outcomes is important to guide clinical decisions and improve care for preterm infants.

5

What are the future directions for research and care regarding chorioamnionitis and premature births?

Future research should focus on understanding the mechanisms by which intrauterine infection/inflammation increases the risk of adverse outcomes for preterm infants. Identifying strategies for maternal care, such as identifying at-risk women and determining the optimal timing for delivery, as well as improving neonatal care, can help improve outcomes for this vulnerable population. Further evaluation is warranted to address the controversies and enhance preventative strategies.

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