Question: when does implantation bleeding happen after frozen embryo transfer?
Answer: Implantation usually is thought to start 6 days after ovulation/retrieval. (In an FET there is no ovulation/retrieval, so it could start 3 days after a 3 day transfer, or the day after a 5 day transfer) You can have menstrual-like cramping and bleeding during implantation, but often it is a silent process.