Placenta implant. When the placenta implants into the inside lining of the uterus it's like a plant growing roots. Maternal blood can leak out during this process and scare women that they may be having a miscarriage. 1st trimester bleeding occurs commonly in 25% of pregnancies, but only results in miscarriage in about half of theses cases. A visit to your OB and a pelvic sonogram is the evaluation needed.
I'd ignore it. 'implantation bleeding' is subtle and unpredictable, if it can be interpreted at all. Internet gossip vastly over-emphasizes the idea of 'implantation bleeding.' implantation always happens 6-7 days after fertilization, so that's the only time you could see it.