Herrera, Enrique, Eduardo Otero, Luis Hincapié, Rafael Camacho, Gustavo Gómez, Carlos Quintero, Célico Guzmán, and Paola Otero. 1. “Heterotopic Pregnancy. Presentation of Four Cases”. Colombia Médica 42 (4), 518-22. https://doi.org/10.25100/cm.v42i4.953.