There is a paucity of evidence that viral infections lead to
preterm labor (10, 19, 22–24); however, there are several areas of
controversy and open questions. For example, what effects do
subclinical viral infections of the decidua and/or placenta during
early pregnancy have in response to other microorganisms, such as
bacteria; and what is the effect of a subclinical viral infection of
the placenta on the fetus?