TABLE 1.

Steps to obtain reliable microbiota*.

1. Larger sample sizes

2. Simultaneous use of different detection methods

3. The elimination of extracellular DNA prior to molecular microbial profiling

4. rigorous controls for reagents and equipment at all steps during sample processing and analysis

5. The determination of the relative abundance of bacterial groups should be preceded by an absolute quantification of the bacterial load in samples and controls

6. Prespecified and quantified bacterial mock communities to the examined samples will help to reveal biases and identify batch effects

7. Demonstration of metabolically active and proliferating diverse bacteria within the placental or fetal tissue will be required to prove the existence of a viable, diverse and unique bacterial community that merits the term microbiota.

8. Taking into consideration geographical, ethnic and societal habits of the population

*This table is adapted from the text and advices provided in Hornef M, Penders J. Does a prenatal bacterial microbiota exist? Mucosal Immunol. 2017 May;10(3):598–601.