Herrera, Enrique, Eduardo Otero, Luis Carlos Hincapié, Rafael Camacho, Gustavo Gómez, Carlos Humberto Quintero, Célico Guzmán, and Paola Otero. 2011. “Heterotopic Pregnancy. Presentation of Four Cases”. Colombia Medica 42 (4):518-22. https://doi.org/10.25100/cm.v42i4.953.