Human Fertilization and Embryogenesis - Online Biology Notes Conception: Meaning in pregnancy and when it happens (medicalnewstoday.com) People usually define conception as the moment when a sperm fertilizes an egg. This can happen inside the body or outside of the body when people are using IVF. However, conception is not a scientific term. It comes from social and philosophical ideas about when human life begins. Some doctors use this word, but others may prefer “fertilization”, which is more specific.