Hustin, J., & Jauniaux, E. (1991). Markedly Elevated Maternal Serum Alpha-fetoprotein Associated With a Normal Fetus and Choriocarcinoma of the Placenta. Obstetrics and Gynecology, 77(2), 329. https://doi.org/10.1097/00006250-199102000-00037 (Original work published 1991)