When does implantation bleeding occur after you've had sex?

Unknown: Implantation bleeding is an unknown and only theoretical entity. There is no science to say it really exists. We occasionally see bleeding in the two weeks after implantation and even further into the first trimester. In our study 60+ % of pts had first trimester bleeding. All of that bleeding is related to "implantation or placental / myometrial invasion" (normal process). Seek help with dr.