When an egg is fertilized just after ovulation, the empty follicle still left guiding (often known as the corpus luteum) carries on to generate progesterone in an effort to maintain the thick uterine lining needed for implantation. In a while in pregnancy, the placenta continues to create the progesterone hormone. http://andreupgqa.educationalimpactblog.com/7066346/rumored-buzz-on-doctor-blake-mysteries