When may a man have intercourse with his wife who lost her fetus in the seventh month and delivered via C-section?

The blood your wife sees after the surgery is postpartum bleeding (nifas (definition)), so intercourse with her is not permissible until it stops. If she becomes pure before forty days, she must perform ghusl (definition) (ritual bath) and becomes like other pure women, and intercourse with her becomes permissible. The preponderant opinion is that it is not disliked to have intercourse with a woman in postpartum bleeding if she becomes pure before forty days. If the bleeding continues after forty days, it is considered irregular bleeding (istihada), so she should perform ghusl and becomes like pure women, and intercourse with her becomes permissible. However, any blood that coincides with her regular menstrual cycle is considered menstruation, during which she should refrain from prayer and fasting, and intercourse with her is forbidden.