Is there really a thing called implantation bleeding?

Yes: Embryo burrows into the decidua (lining of the uterus during early pregnancy) for implantation and the process can result in a slight bleeding.

Implantation bleed: Absolutely, it happens about 4-6 days after ovulation.

Implantation Bleed: Implantation bleeding is real, typically a small amount of spotting 2 wks after fertilization (at the time of the missed menstrual period). The fertilized egg disrupts the decidua (vessels/fertile lining) of the uterus and causes a small bleed. Larger bleeds are more likely miscarriages, polyps, infection, or ectopic pregnancies.