Complex sentence: It was not until the late twentieth century that a medical specialist, Professor of Gynecology, Yves Malinas, conducted a study of the autopsy and according to his study, Marie Angélique died of cancer of the fetal membrane.
Split into simpler sentences: It was not until the late twentieth century that a medical specialist, Professor of Gynecology Yves Malinas, conducted a study of the autopsy. According to him, Marie Angélique died of cancer of the fetal membrane.