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Movies like Polygyny (1999)

A married couple desperate to conceive a child of their own is given an unexpected solution to their dilemma. The husband's adulterous affair with another married woman results in the birth of an illegitimate child. The husband proposes that he and his wife permanently raise the new born, under the stipulation that she (the mistress) promises to never see her child and accepts the monetary compensation provided. But this agreement is broken and the story takes a dramatic turn for the worst.