Fertilization occurs when the sperm meets the egg. As soon as this happens, cell division begins. Baby is now called a zygote. After the sperm and egg’s nuclei merge, the zygote begins its 3-4 day trip down the fallopian tube to the uterus. Within another 2 days or so, your baby is now called a blastocyst and implants itself into your uterine wall. This may or may not be accompanied by light spotting.