I looked up the canons:
St John: 17. As for women occupying a separate seat, let them not touch holy things for as many as seven days, the second Canon of St. Dionysius, but in particular the seventh Canon of Timothy bids. This is also what the old Law ordered, but neither did it permit them to have any sexual intercourse with men; for it happens on this account that the seeds sown become weak and evanescent. Hence it was that divine Moses ordered the father of a defective to be stoned to death, on the ground that on account of his intemperance he failed to await the purification of his wife. But as for a woman who has been so scornful of the same uncleanness during this period and has touched the divine Mysteries, they bid her to remain communionless for forty days.
The present Canon decrees that those women shall not participate in the divine Mysteries who are having their usual trouble of courses and menstruation, or what are commonly called “monthlies,” for at least seven days, just as c. II of Dionysius also decrees, and c. VII of Timothy commands. This same prohibition is found in the old Law, which does not permit such women to have sexual intercourse with their husbands so long as they are having their monthlies, because even the children that are sown and conceived in women who are in such a condition become in consequence weak and defective for the most part. It was for this reason, too, that the Law commanded that the father of a defective child be stoned to death, since on account of his wanton lust he did not have the fortitude to wait for his wife to be purified from monthlies, but slept with her while she was having them, and thus the child sown in her became defective. But if a woman having her monthlies scornfully disregard this fact and partake of the divine Mysteries, they command that she shall not commune again for forty days. Read also c. II of Dionysius.
St Dionysius: 2. Concerning menstruous women, whether they ought to enter the temple of God while in such a state, I think it superfluous even to put the question. For, I opine, not even they themselves, being faithful and pious, would dare when in this state either to approach the Holy Table or to touch the body and blood of Christ. For not even the woman with a twelve years’ issue would come into actual contact with Him, but only with the edge of His garment, to be cured. There is no objection to one’s praying no matter how he may be or to one’s remembering the Lord at any time and in any state whatever, and petitioning to receive help; but if one is not wholly clean both in soul and in body, he shall be prevented from coming up to the Holies of Holies.
When asked about this too, as to whether women in their menses ought to enter the temple of God, the saint replied that there is no need of asking the question, since if the women themselves have a proper reverence for things divine, they will be inhibited by it from daring ever to approach the Holy Table and to partake of the Lord’s body and blood when they are in such a state of their menstrual affairs. For they can recall that woman who had an issue of blood and who on account of the flux of her blood did not dare, because of her great reverence, to touch the body of Christ, but only the hem of His garment. None of them is forbidden to pray, whatever be her predicament (whether she be at home or in the pronaos of the church), by imploring God and asking Him for help and salvation. One is forbidden, however, to go near the Holies of Holies, which is the same as saying to partake of the sanctified portions (i.e., the Eucharistic species) when he is not clean in soul and body, like women who are taken with their menses.
Timothy: 7. Question: If a woman finds herself in the plight peculiar to her sex, ought she to come to the Mysteries on that day, or not?
Answer: She ought not to do so, until she has been purified.
Likewise as in the above Canon, the present Canon decrees that a woman must not partake of the divine Mysteries on the days on which she is troubled by the plight pertaining to her sex, but only to partake thereof when she has been purified from it. See also c. II of Dionysius.