Contrary to the findings of recent studies, the human fetus and its prenatal intrauterine environment are not stably colonized by microbial communities, according to research newly published in Nature this week. The concept of a fetal microbiome, which would have significant implications for clinical medicine, is a subject of much debate. In the new analysis, a team led by scientists from University College Cork examined studies characterizing microbial populations in human fetuses from the perspectives of reproductive biology, microbial ecology, bioinformatics, immunology, clinical microbiology, and gnotobiology, and assessed possible mechanisms by which the fetus might interact with microorganisms. They determine that a healthy human fetus is sterile and that previously detected microbial signals in the womb likely resulted from contamination during the clinical procedures to obtain fetal samples or during DNA extraction and DNA sequencing. "The pursuit of a fetal microbiome serves as a cautionary example of the challenges of sequence-based microbiome studies when biomass is low or absent, and emphasizes the need for a trans-disciplinary approach that goes beyond contamination controls by also incorporating biological, ecological, and mechanistic concepts," the authors write.