Why is the safe period not always safe

Patient's question:

No

Doctor's answer:

!The safe period is to avoid the4-5 days before and after the regular ovulation period, which is 8 days after menstruation and 7 days before menstruation. The success rate is only 80%. The ovulation process in women can be affected by life, emotions, sexual activity, health status, and external environment, causing it to be advanced or delayed. It may also lead to additional ovulation, so it is not very reliable, with a failure rate of 20%.