I had implantation bleeding 10 days after I had in vitro. I was taking a shower and had all this red blood. It seemed like a ton because of the water. I thought it was my period and wore a tampon, but it got light super quick (like the next day.) I had to go take a pregnancy test the next day just to make sure and when they called me to say I was pregnant all I could say was, "but I'm wearing a tampon." It was different than my period because there was no brown blood, just bright red and it was one gush then real light.