What immunological and hormonal protective factors lower the risk of COVID-19 related deaths in pregnant women?

Despite anticipated increased risk of COVID-19 and increased expression of the SARS CoV-2 receptor (ACE2), the relatively low mortality of pregnant women with COVID-19 has been an area of wonder. The immunological changes predominantly inclining to anti-inflammatory state, which is augmented by placental hormones' immune modulating action, looks against with COVID-19 inflammatory reaction leading to cytokine storm and multiple organ failure. Unlike many other viral infections, the bilateral immune activation of COVID-19 may preferentially make pregnant women at low risk. Taking the physiological advantage of pregnant women, potential clinical trials are proposed. Quite a large number of epidemiological and obstetrics related studies have addressed the cases of women with COVID-19. However, to the best of the author's knowledge, little is done to explore the physiological internal milieu of pregnant women in relation to COVID-19. This review provides an insight into how the hormonal and immunological changes in pregnancy potentially reduce SARS-CoV-2-mediated inflammatory response.