Fertilization itself happens not always right after unprotected sex. The sperm is ‘active’ approximately 72 hours. So, it takes from several hours to 3 days for ovum to become a blastocyst. The next step of the fertilized ovum is to move down the fallopians towards the uterus. Implantation bleeding happens, when blastocyst implants into the inner surface of the womb. Spotting starts on the 6-12th day after conception.
From the moment of implantation blastocyst becomes a full-fledged embryo. It is safely linked with mother’s organism. Woman’s body can’t keep silence, it gives a first reaction. More than 30% of future moms experience such a phenomenon as middle-cycle bleeding (scientifically called implantation bleeding) and implantation cramps. Bloody discharge lasts from several hours to several days. Normally it stops in 48 hours.