Whether a developing baby (the fetus) has a microbiome or whether it is sterile during pregnancy and only gets "seeded" by microbes from the mother during birth is still being hotly debated. For years it was thought that the fetus and placenta were sterile (no microbes), but then several studies said there is evidence for the fetus and placenta having a microbiome (community of microbes).
Recently an international group of researchers stated that NO, there is no fetal microbiome. They reviewed current evidence, and according to their opinion - a healthy fetus is sterile. Instead, they suggest that the microbes some researchers found were due to contamination when the samples were taken or during analysis.
We'll see how this all develops. Science is always evolving, with new findings, and lots of debate and controversy.
From Medical Xpress: Expert analysis refutes claims that humans are colonized by bacteria before birth
Scientific claims that babies harbor live bacteria while still in the womb are inaccurate, and may have impeded research progress, according to University College Cork (UCC) researchers at APC Microbiome Ireland, a world-leading Science Foundation Ireland (SFI) Research Center, which led a perspective published today in the journal Nature.
Prior claims that the human placenta and amniotic fluid are normally colonized by bacteria would, if true, have serious implications for clinical medicine and pediatrics and would undermine established principles in immunology and reproductive biology.
To examine these claims, UCC & APC Principal Investigator Prof. Jens Walter assembled a trans-disciplinary team of 46 leading experts in reproductive biology, microbiome science, and immunology from around the world to evaluate the evidence for microbes in human fetuses.
A healthy human fetus is sterile
The team unanimously refuted the concept of a fetal microbiome and concluded that the detection of microbiomes in fetal tissues was due to contamination of samples drawn from the womb. Contamination occurred during vaginal delivery, clinical procedures or during laboratory analysis.
In the report in Nature, the international experts encourage researchers to focus their studies on the microbiomes of mothers and their newborn infants and on the microbial metabolites crossing the placenta that prepare the fetus for post-natal life in a microbial world.
According to Prof. Walter, "This consensus provides guidance for the field to move forward, to concentrate research efforts where they will be most effective. Knowing that the fetus is in a sterile environment, confirms that colonization by bacteria happens during birth and in early post-natal life, which is where therapeutic research on modulation of the microbiome should be focused."