Divorce during the menses is counted as one legal divorce.

Sahih al-Bukhari · Book 68 · Hadith 5252

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا شُعْبَةُ، عَنْ أَنَسِ بْنِ سِيرِينَ، قَالَ سَمِعْتُ ابْنَ عُمَرَ، قَالَ طَلَّقَ ابْنُ عُمَرَ امْرَأَتَهُ وَهْىَ حَائِضٌ، فَذَكَرَ عُمَرُ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ ‏"‏ لِيُرَاجِعْهَا ‏"‏‏.‏ قُلْتُ تُحْتَسَبُ قَالَ ‏"‏ فَمَهْ ‏"‏‏.‏ وَعَنْ قَتَادَةَ عَنْ يُونُسَ بْنِ جُبَيْرٍ عَنِ ابْنِ عُمَرَ قَالَ ‏…

Narrated Anas bin Seereen: Ibn `Umar said: "I divorced my wife while she was menstruating. `Umar mentioned that to the Prophet . The Prophet (ﷺ) said, (to my father), "Let your son take her back." I asked (Ibn `Umar), "…

Sahih al-Bukhari · Book 68 · Hadith 5253

وَقَالَ أَبُو مَعْمَرٍ حَدَّثَنَا عَبْدُ الْوَارِثِ، حَدَّثَنَا أَيُّوبُ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عُمَرَ، قَالَ حُسِبَتْ عَلَىَّ بِتَطْلِيقَةٍ‏.‏

Narrated Ibn `Umar: (Divorcing my wife during her menses) was counted as one legal divorce.