Rule [ 9]
وَاللَّائِي يَئِسْنَ مِنَ الْمَحِيضِ مِن نِّسَائِكُمْ إِنِ ارْتَبْتُمْ فَعِدَّتُهُنَّ ثَلَاثَةُ أَشْهُرٍ وَاللَّائِي لَمْ يَحِضْنَ ۚ وَأُولَاتُ الْأَحْمَالِ أَجَلُهُنَّ أَن يَضَعْنَ حَمْلَهُنَّ
(And those women from among you who have despaired of [ further ] menstruation, if you are in doubt, their "iddah is three months, as well as of those who have not yet menstruated. As for those having pregnancy, their term [ of "iddah ] is that they give birth to their child…65:4)
This verse deals with additional rules pertaining to the waiting-period of divorced women. It subdivides divorced women and their waiting-periods into three different categories. Under normal circumstances, the waiting-period of a divorced woman is three menstrual cycles as mentioned in Surah Al-Baqarah. In the case of women who have stopped menstruating for good on account of advanced age, or due to some disease etc. their "iddah is three months instead of three menstrual cycles. The same is the "iddah of young women who have not yet started menstruating on account of being under age. The "iddah for women who are pregnant at the time of divorce continues until they give birth to their child irrespective of the length of the period.
The words o (if you are in doubt) refer to the doubt or confusion such women may have because the real "iddah is counted on the basis of menstruation, but these women's menstruation has ceased, so they are doubtful about how to count their 'iddah.
وَمَن يَتَّقِ اللَّـهَ يَجْعَل لَّهُ مِنْ أَمْرِهِ يُسْرًا (And whoever fears Allah, He brings about ease for him in his affair….65:4) The verse further speaks of the virtues and blessings of taqwa in that whoever has taqwa, Allah will make matters easy for him in this world as well as in the next world.