One of the correspondents on the ‘phemonena’ website is Carl Zimmer, who has a newish column at the NY Times about the findings which show that the fetus is not sterile. This is not completely new, but I think it is still not well understood. I thought until recently that the fetus and placenta were bug-free, but data a couple of years ago about placental PCR analysis showing lots of bugs, especially from premature deliveries made it clear that I had been mis-informed.

This article is a good introduction for the non-specialist.