Slightly OT, but since you brought it up... most of the cases in which women haven't known they were pregnant either seemed to be that the woman wasn't surprised not to be menstruating (she was breastfeeding, or she was older and thought she was in early menopause) or that the woman was in the uncommon but not totally rare situation where she continued to have what are similar to menstrual periods during her pregnancy. Some women also don't gain a lot of weight, or are somewhat overweight to begin with and don't gain a lot of additional weight, or they're on a medication that they attribute the weight gain to, things like that.
Our Freecycle has been a bit frustrating lately. First, they have a rule that you can only post a WANTED once a week. So I posted one, then a while later I posted another, and got a warning from a moderator that I wasn't following the rules for WANTEDs. So I checked... my posts were 8 days apart. One on Sunday, one the following Monday. Couldn't figure out how I violated the rules. Oh, well. Then I notice that they've been posting the rules every week, claiming that there have been a lot of violations, etc., and reminding people of the rules. One of which is to include your location in your offer. Posts must be moderated before they get posted. And yet I saw an offer that looked interesting the other day, but it didn't have a location. So I don't know what's going on with the moderation, but something sure is.