Does the divorce of a pregnant woman take effect if neither she nor her husband knew of her pregnancy, and is it permissible for her husband to take her back after divorcing her for the third time and her giving birth to a male child, without her marrying another man, believing that this child makes up for that?

Divorce of a pregnant woman is valid and binding, whether the husband knows about it or not. If it is the third divorce, she is not permissible for him until she marries another husband, and pregnancy does not suffice in place of that. There is no disagreement among the scholars regarding the validity and binding nature of divorcing a pregnant woman, and that knowledge of it or lack thereof is not taken into consideration.