When a fertilized egg arrives in the uterus, the lining must be precisely prepared to receive it. If the egg is released too soon or too late, the uterus lining will be either too immature or too ripe for implantation. The fertilized egg cannot survive unless it becomes implanted in the uterus, and will be shed. It can be seen that the timing of ovulation is a critical factor for successful implantation.

One early warning signals that ovulation might be occurring too early or too late is irregular periods. Another warning signal is a lack of copious and watery mucus at mid-cycle. Anovulation, no egg production, is an obvious cause of infertility. This can also show as very irregular periods. Painful cramps during a period are not implicated in early or late ovulation, nor has PMS been found to be involved. If any of the warning signals are present, visit the fertility clinic without delay. Fertility drugs can be effective in the management of irregular periods.