The most common cause of intrauterine fetal demise (IUFD) in developed countries is unexplained fetal death. Despite thorough investigations, a significant proportion of IUFD cases remain idiopathic, with no definitive cause identified. This is due to the complex interplay of multiple subtle factors that can be difficult to detect, including genetic, placental, and maternal conditions. Other identifiable causes like placental abruption, maternal diabetes, and infection are less frequent. Recognizing that unexplained IUFD accounts for up to 40-50% of cases is crucial in clinical practice for counseling and managing future pregnancies.

Reference: Williams Obstetrics, Cunningham FG, 25th Edition.