In recent years, a few studies have challenged this concept by reporting traces of microbial DNA in supposedly sterile tissues like amniotic fluid, umbilical cord blood, and the placenta – but these results are highly controversial.12 It’s not clear how these microbes get there, whether their presence matters, or if they actually exist – the DNA could have come from dead cells, or from bacteria that contaminated the experiments. Tissier’s sterile womb hypothesis might be wrong, but it certainly hasn’t toppled yet.
