Jo- I had a really obvious one with DS but nothing at all with my second prenancy that I lost (also a little boy) . I was convinced that it was going to be a BFN becasue I hadn't had the bleed, but I was wrong. That baby was totally healthy and growing perfectly until 12 weeks as well and we don't know why he died so I honestly don't think there was any difference in implanting etc, it was just something that happened much later.