The Placental Microbiome: A Whole World Unto Itself

By Eva Martin, MD of Elm Tree Medical Inc.

Chorioamnionitis literally means infection of the chorion and amnion, the membranes that surround a fetus in the uterus. But what causes it? And what does it cause? New research is showing that the microbiome, or unique bacterial community, living on those membranes is intricately tied to the development and severity of chorioamnionitis. Furthermore, the metabolism of the bacteria in the microbiome differ for those with and without chorioamnionitis. 

Researchers at Baylor College of Medicine in Houston recently undertook a study to explore the microbiome of the membranes around the placenta for infants with and without chorioamnionitis. Because chorioamnionitis is linked to some preterm births, the researchers also compared infants born at term (greater than 37 weeks of pregnancy) and those born preterm. Right after the babies in the study were delivered, the doctors took a swab of the membranes around the placenta and then analyzed the bacterial DNA on the swab using "state-of-the-science" techniques.

Chorioamnionitis can vary in severity. To diagnose and grade the severity of chorioamnionitis, pathologists examine the placental membranes under a microscope. Each case of chorioamnionitis for infants born preterm in the study was graded as mild, severe, or accompanied by funisitis. Funisitis is inflammation of the tissues of the umbilical cord, and was the most severe grade of infection in the study. The researchers found that the microbiome was different, depending on how severe the chorioamnionitis was. However, perhaps most interestingly, infants treated with steroids (betamethasone) or antibiotics during labor did not have different microbiomes from those not treated with these medications.

For infants with chorioamnionitis who were born preterm, they researchers found a lot of urogenital and oral bacteria. They also found significant differences in the the metabolic pathways of the bacteria they found. For infants born preterm with chorioamnionitis, there were differences in the bacteria's fat and protein metabolism. For infants born at term with chorioamnionitis, there were differences in the bacteria's sugar metabolism.

The authors conclude that pregnancies that suffer from chorioamnionitis have different microbiomes living on the placental membranes, and those bacterial communities have different metabolic make-up. These differences may determine the pregnancy's risk of chorioamnionitis and severity of chorioamnionitis. For my 2 cents, I hope that they conduct further research to learn why antibiotic treatment did not influence the bacteria of the microbiome.