Women's wombs full of good germs, not bacteria-free after all, study finds

Surprising new research shows a small but diverse community of bacteria lives in the placentas of healthy pregnant women, overturning the belief that fetuses grow in a sterile environment.

These are mostly varieties of "good germs" that live in everybody. But Wednesday's study also hints that the make-up of this microbial colony plays a role in premature birth.

"It allows us to think about the biology of pregnancy in different ways than we have before, that pregnancy and early life aren't supposed to be these totally sterile events," said lead researcher Dr Kjersti Aagaard of Baylor College of Medicine in Houston.

All humans share their bodies with trillions of microbes on the skin, in the gut and in the mouth. These communities are called the microbiome. Many bacteria play critical roles in keeping us healthy. The Human Microbiome Project in the US mapped what made up these colonies and calculated that healthy adults cohabitated with more than 10,000 species.

Healthy newborns pick up some from their mother during birth but there have been some signs that the process could begin in-utero.

"We have traditionally believed in medicine that the uterus is a sterile part of the human body," said Dr Lita Proctor of the National Institutes of Health, who oversaw the microbiome project.