Is it true that pregnancy does not occur if sexual intercourse takes place between spouses 4 or 5 days before menstruation, and how can one calculate the days of the cycle and the next menstruation if it is regular (28 days)?

The prescribed greeting of peace is "As-salamu alaykum" and "Rahmatu Allahi wa barakatuh" (the mercy of Allah and His blessings be upon you). There is no knowledge that intercourse 4 or 5 days before menstruation prevents pregnancy; it is advised to consult a doctor. The days of menstruation are known to women, and during them, prayer, fasting, and intercourse are abandoned. The minimum period of purity between two instances of bleeding and the maximum duration of menstruation is fifteen days according to the majority of scholars.