I always seem to start bleeding/spotting on Day 12 (2 days before test date). Even on my first +ve cycle I started spotting (thought this turned to full AF after a +ve HCG test). On my 2nd negative cycle I again started spotting on Day 12 followed by full AF on Day 13/14.
jg:
I had 3 embryos transferred and 1 implanted. I never bleed out the 2 lost embryos or noticed anything. My doctor said I probably would not notice them and I would never know they were gone. I did experience a little bit of spotting about 1 week after my +ve which was just some left over blood from the implantation.
Good luck!
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