Some scientists say that implantation is when and where pregnancy begins. What is implantation and are there any common signs of implantation? Implantation occurs when the egg that has been fertilized by the sperm attaches to the inner wall of the uterus about 7-9 days after conception. Having traveled down the fallopian tube and divided several times, the fertilized zygote has reached its final destination in the warm and nourishing uterine lining. Now it can receive the oxygen and nutrients from mom to begin to grow and develop into the beautiful baby it will become. Implantation must occur for pregnancy to continue.