Someone asked about this possibly being caused by a hormonal
transition(something like that).

The Maternity Sourcebook, by Wendy and Matthew Lesko, states "Some
miscarriages that occur toward the end of the third month are the result
of the transitional period of the embryo's support system. At this stage
the corpus luteum (which is responsible for the baby's growth until the
placenta takes over) shrivels up, and the transference does not always
progress smoothly."
This topic really hit home with me, since in two of my pregnancies I
experienced bleeding at 14 wks. (now the bleeding I had at 20 wks, this
would not explain.) Very scary experiences, but everything ended up
being okay.

Ellen in Pittsburgh