The scholars differed as to whether the divorce of a menstruating woman counts as such or not. The majority believe that Talaq counts as such. Still, there is a minority group who says that it does not, and this is the view reflected in the fatwas of many contemporary scholars nowadays.
Allah decreed that a woman should be divorced when she is in a state of purity, free from nifaas (postpartum bleeding) and menses, and during a time of purity when her husband has not yet had intercourse with her.
Allah says (what can be translated as):
“O Prophet! When you divorce women, divorce them at their ‘Iddah (prescribed periods) and count (accurately) their ‘Iddah ” [al-Talaaq 65:1]
The verse means that the wives are pure (not menstruating) and husbands have not had intercourse with them.
The above interpretation is what the scholars have said about divorcing them at their prescribed periods. When the husband announces Talaq, the wives should be pure (not menstruating), and you should not have had intercourse with them at the time of Talaq, or they should be pregnant.