Ferrer-Oliveras et al researched the harm that COVID-19 incurs on patients and the bidirectional relationship between COVID-19 and pregnancy. They proposed a four-stage model for the clinical steps of the disease: Incubation (0), Early Infection (1), Primary Inflammatory Response (2), Secondary Inflammatory Response (3), and Immune Protection (4). During Stage 0, the S-protein is cleaved into S1 and S2 which interacts with ACE2 receptors and the membrane respectively; there are no symptoms. These receptors are found in the lung, heart, liver, kidney, and bowel. Stage 1 is when there is viral replication and the mature virion RNA enters the endosome triggering inflammatory responses, which leads to mild symptoms. Stage 2 is when the innate immune system and adaptive immune system are activated leading to potential pulmonary complications, hypoxia, and dyspnea. Stage 3 is the secondary inflammatory response, with macrophages, thrombosis, and cytokine storms which could lead to myocarditis or thrombosis. Stage 4 is post infection, with a reduced inflammatory response which leads to recovery. It was found that pregnant women experience greater COVID-19 viral associated morbidity and mortality compared to non-pregnant women. The researchers found that COVID-19 may induce more miscarriages in the first and third trimester, or fetal defects in the second trimester. Additionally, COVID-19 could increase thrombotic tendencies and induce the hyperinflammation in pregnant women via the complement system. The researchers urge obstetricians and immunologist to document disease outcomes in pregnant women to further understand how COVID-19 might impact them.