Anfuso, S., et al. “Second-Trimester Maternal Serum Alpha-Fetoprotein Elevation and Its Association With Adverse Maternal Fetal Outcome: Ten Years Experience”. Acta Biomedica Atenei Parmensis, vol. 78, no. 3, Dec. 2007, pp. 214-9, https://mattioli1885journals.com/index.php/actabiomedica/article/view/1905.