I would like you to confirm exactly what you said, and ask you what mechanisms may be involved. Two years ago I would not have believed this new concept. There are a number of animal studies, and now more and more human studies, to support the conclusion that the cytokines from the maternal-antipaternal immune response are a driving force during pregnancy. They stimulate placental formation. The decidua is prepared by cytokines to receive the blastocyst.
Cytokines finally induce the production of the prostaglandins that result in delivery.
IL-8 comes in both at menstruation and at delivery, so that a lot of neutrophils come in, surely to defend the bleeding surfaces open to infections, but also to provide the collagenase that opens up the cervix. It all comes together in a most remarkable way.