About a research:

Dear brothers, this is about a research done by a Muslim physician. If it is a well-known fact that there can be no pregnancy with menstruation, nor can be menstruation with pregnancy, why Allay says:

﴾ And divorced women shall wait (as regards their marriage) for three menstrual periods, and it is not lawful for them to conceal what Allah has created in their wombs, if they believe in Allah and the Last Day. ﴿

[ Al-Baqarah, 228 ]

This physician discovered rare cases when a woman might have her period once or twice at the beginning of her pregnancy. The pregnancy doesn't show clinically at its early stages but at advanced stages it becomes obvious to the mother, the physician and the husband.

Since science proved that in rare cases a woman might have her period once, twice or thrice at the beginning of her pregnancy for scientific reasons which we don't have time to mention, then this Ayah, and the Divine command within, gives the woman enough time to make sure if she is pregnant or not. The absence of the menstruation most likely denotes pregnancy, but is it enough evidence? According to physicians and their experiences, no it is not enough.

﴾ And divorced women shall wait (as regards their marriage) for three menstrual periods, and it is not lawful for them to conceal what Allah has created in their wombs, if they believe in Allah and the Last Day.  ﴿

[ Al-Baqarah, 228 ]

 In order to help us know that Islamic Religion is from the Lord, Allah, Creator of all worlds, in order to help us know that such uncommon cases among pregnant women really exist, and in order to help doctors, particularly obstetricians, know such rare cases, this Ayah from Allah refers to this fact.