Ríos, Juan Carlos, Juan Guillermo McEwen, Adriana Cuartas, Fanny Cuesta, and Sergio Parra. 2008. “Role of Four Polymorphisms of the β-2 Adrenergic Receptor Gen in Patients With Preterm Delivery”. Colombia Medica 39 (1):7-15. https://doi.org/10.25100/cm.v39i1.545.