at the cycle in the diagram in question .
the first stage that will not happen if the egg cell is fertilised.

When an egg cell is fertilised, it triggers a series of changes that prevent the first stage of the menstrual cycle—ovulation—from occurring. Ovulation typically involves the release of an egg from the ovaries, but if fertilisation occurs, hormonal signals communicate to the body to maintain the thickened uterine lining instead. This is the magic that keeps the egg safe and snug, preparing the body for potential pregnancy!

In addition, once fertilisation takes place, the developing embryo releases human chorionic gonadotropin (hCG), which is crucial for maintaining the corpus luteum. This structure produces progesterone, preventing the shedding of the uterine lining until the embryo has implanted properly. So, no ovulation means no month-long cycle reset, and a potential bump in nine months instead!