Human placenta has no microbiome but can contain potential pathogens.

Abstract

We sought to determine whether preeclampsia, delivery of a small for gestational age infant or spontaneous preterm birth were associated with the presence of bacterial DNA in the human placenta. Here we show that there was no evidence for the presence of bacteria in the large majority of placental samples, from both complicated and uncomplicated pregnancies. Almost all signals were related either to acquisition of bacteria during labor and delivery or contamination of laboratory reagents with bacterial DNA. The exception was the detection of Streptococcus agalactiae (Group B Streptococcus), where non-contaminant signals were detected in ~5% of samples collected prior to the onset of labor. We conclude that bacterial infection of the placenta is not a common cause of adverse pregnancy outcome and that the human placenta does not have a microbiome, but it does represent a potential site of perinatal acquisition of Streptococcus agalactiae, a major cause of neonatal sepsis. An Author Correction to this article has been published; see journal website.