What is the Sharia ruling on divorcing a second wife three times, two of which occurred in a single sitting, knowing that she was pregnant, and is it permissible to marry her again after her 'tahlil' marriage to another man?

Allah has permitted a man to marry up to four women and has placed divorce in his hands. Therefore, you are entitled to marry more than one, and you are not obligated to obey your first wife regarding the divorce of the second. What you did in divorcing the second wife renders her irrevocably divorced (thrice-divorced) according to the majority of scholars. Your agreement with the second wife for the purpose of her marrying another man, who then divorces her before consummation, is forbidden. She is not lawful for you until she marries another man in a valid marriage, with the intention of desire and enduring companionship, and actual consummation. Then, if he divorces her thereafter and her waiting period (iddah) concludes, it becomes permissible for you to marry her.