What happens when the ovum is fertilized?

If the ovum is fertilized, there is no breakdown of endometrium and no menstrual flow. The fertilized ovum travels through uterine tube to the uterus where it becomes embedded in the wall and produces chorion gonadotrophins. This keeps corpus luteum intact enabling it to continue to secrete progesterone for the first 3-4 months of pregnancy, inhibiting the maturation of ovarian follicles. During that time, placenta develops and produces oestrogen, progesterone and gonadotrophins. The placenta provides an indirect link between the circulation of the mother and that of the foetus. Through the placenta, the foetus obtains maturational materials, O₂, antibodies and gets rid of CO₂ and other waste products.