Sydney: Doctors will now be able to identify early on whether a mother will develop pre-eclampsia, the most common and severe pregnancy-related disease, a study says.

"It develops in mothers out of the blue, usually in the last three months of pregnancy, causing high blood pressure, kidney and liver damage and severe blood changes," said Ralph Nanan, professor from the University of Sydney Medical School Nepean, Australia, who co-authored the study with David Eviston, Ann Quinton and colleagues, the Journal of Reproductive Immunology reports.

The findings suggest that pre-eclampsia cannot be diagnosed by symptoms before the disease occurs, which may have a lasting impact on a child's immune system.

"Pre-eclampsia affects an estimated 5,000 to 10,000 women in Australia every year. Delivering the baby as soon as possible is the only way to stop it. In pre-eclampsia the mother's immune system appears to attack the foetus," added Nanan, according to a Sydney statement.

"Our study looked at the thymus of the foetus, a structure which sits behind the baby's breastbone and is known as the 'cradle' of an important set of white blood cells called thymus-derived lymphocytes or T cells," said Nanan.

"Surprisingly, we found the thymus of babies whose mother developed pre-eclampsia was significantly smaller than in babies of healthy pregnant women."

What further surprised the researchers was that these changes were obvious in mid-pregnancy, long before the mother developed any signs of pre-eclampsia.

"This is a very interesting finding as the thymus plays a central role in shaping the child's immune system and protecting it against the development of allergies, autoimmune disease and cancers later in life," Nanan said.

The group is now conducting a prospective study with over 1,200 pregnant women to confirm the findings with the long-term prospect of developing a test for pre-eclampsia.