Theprocess of embryo implanting usually takes place around the 6th day after fertilization of the sperm and egg. After the fertilization of the egg, the zygote slowly starts to slowly emit the hCG hormone. In the beginning, it’s measurements are so small that the hCG levels are not high enough to register on any pregnancy test (unless the IVF process used involves a starter hormone injection). HCG levels double in amount every 72 hours and peaking at around 8 to 11 weeks of the pregnancy. This is why waiting for this hormone to grow can be agonizing, but at the same time is necessary.