Question: how many days after fertilization does the blastocyst start to implant in the endometrium?
Answer: Implantation. Once the embryo reaches the blastocyst stage, approximately five to six days after fertilization, it hatches out of its zona pellucida and begins the process of implantation in the uterus. In nature, 50 percent of all fertilized eggs are lost before a woman's missed menses.