Many authorities would say that the chances are much less than the figures given. Alternatively, if they have had intercourse on the most fertile day they should not expect pregnancy to follow as a certainty. There are six main methods by which ovarian activity can be monitored and the time of ovulation determined. Every women is taught to document her bleeding pattern and this is the method used to assess ovarian activity since the human race began. Onset of vaginal bleeding is used to mark menarche and its cessation marks the menopause.
Pregnancy is indicated when regular menstruation stops abruptly.
It usually results from withdrawal of oestrogen and progesterone activity at the end of an ovulatory cycle. Such bleeding is called menstruation. Bleeding can also be the result of oestrogen activity alone produced by an ovarian follicle which has not ovulated. This is called anovulatory bleeding. Bleeding is the end result of the ovarian activity, it gives little information about the ovarian events which have preceded it and it occurs at variable levels of hormone withdrawal.