The womb has long been considered a sterile environment. A baby’s debated first exposure to microbes, at birth, appears to play a critical role in postnatal immune development. Babies born vaginally, and thus exposed to the mother’s microbiome, were found to develop stronger immune systems than babies born by Cesarean-section. Raising the possibility that microbes are present in the intrauterine environment, several groups isolated microbes from placentas and fetal meconium. However, some researchers question whether the samples or reagents were  contaminated. Isolating a sterile sample from any environment would be tricky, and even more so during birth. Since the purity of the aforementioned samples is questionable, some groups are investigating how microbes might enter the uterus during pregnancy.  Could intrauterine microbes come from the reproductive tract, invasive medical  treatments, or maternal gastrointestinal stress? Others wonder what role microbes in the uterus could play in fetal development or preterm births. 

With few standing microbe-free areas of the body, a uterine microbiome seems realistic. Nonetheless, at this point, I think it’s more important to establish reliable methods for isolating pure uterine samples than to invest resources in potential effects of the microbes.