Pregnant women infected by the novel coronavirus run a higher risk of developing pre-eclampsia, according to a review of the scientific literature by Brazilian researchers.

Pre-eclampsia is a pregnancy complication characterised by persistent high blood pressure, usually in the second half of pregnancy or shortly after delivery. The disorder can cause serious harm to mother and baby.

The review published in the journal Clinical Science, analysed a large set of published data and concluded that infection by SARS-CoV-2 during pregnancy can reduce the availability of ACE2, a protein that plays an important part in placental development, control of blood pressure, and the circulatory adaptations required for foetal development.

ACE2 is also the protein to which SARS-CoV-2 binds in order to invade cells.

Alterations in levels of ACE2 impairs the functioning of systems that depend on ACE2 to regulate blood pressure.

"Based on the findings of studies conducted to date on infection by SARS-CoV-2 in pregnant women and the role of ACE2 in the placenta, it can be concluded that pregnant women run a higher risk of developing the severe form of Covid-19 than non-pregnant women," said Nayara Azinheira Nobrega Cruz, who led the study as part of her doctoral research at the Federal University of Sao Paulo's Medical School (EPM-UNIFESP).

Apart from the fact that ACE2, the receptor for SARS-CoV-2, is abundant in the placenta, the researchers found that the incidence of severe Covid-19 among pregnant women could be due to inhibition of the enzyme's action by the viral infection.

Because the virus uses it to invade cells, infection probably reduces the availability of ACE2 and its capacity to protect the organism during pregnancy.

"A deficit of ACE2 can cause an imbalance in the renin-angiotensin system and an increase in the peptide angiotensin 2, a vasoconstrictor, driving up the mother's blood pressure and leading to pre-eclampsia," said Dulce Elena Casarini, Department of Medicine, Federal University of Sao Paulo.

The researchers stressed that further research is needed to determine with greater precision why pregnant women are more susceptible to Covid-19, and the role played by the disease in pre-eclampsia.

They are collecting samples of placenta from women infected by the virus in order to perform a series of experiments to find out what is really happening.

Besides pre-eclampsia, they are interested in the role of infection by the novel coronavirus in placental inflammation and vascularisation.